1
        2
        3
        4
        5
        6
        7
        8
        9
       10
       11
       12
       13
       14
       15
       16
       17
       18
       19
       20
       21
       22
       23
       24
       25
       26
       27
       28
       29
       30
       31
       32
       33
       34
       35
       36
       37
       38
       39
       40
       41
       42
       43
       44
       45
       46
       47
       48
       49
       50
       51
       52
       53
       54
       55
       56
       57
       58
       59
       60
       61
       62
       63
       64
       65
       66
       67
       68
       69
       70
       71
       72
       73
       74
       75
       76
       77
       78
       79
       80
       81
       82
       83
       84
       85
       86
       87
       88
       89
       90
       91
       92
       93
       94
       95
       96
       97
       98
       99
      100
      101
      102
      103
      104
      105
      106
      107
      108
      109
      110
      111
      112
      113
      114
      115
      116
      117
      118
      119
      120
      121
      122
      123
      124
      125
      126
      127
      128
      129
      130
      131
      132
      133
      134
      135
      136
      137
      138
      139
      140
      141
      142
      143
      144
      145
      146
      147
      148
      149
      150
      151
      152
      153
      154
      155
      156
      157
      158
      159
      160
      161
      162
      163
      164
      165
      166
      167
      168
      169
      170
      171
      172
      173
      174
      175
      176
      177
      178
      179
      180
      181
      182
      183
      184
      185
      186
      187
      188
      189
      190
      191
      192
      193
      194
      195
      196
      197
      198
      199
      200
      201
      202
      203
      204
      205
      206
      207
      208
      209
      210
      211
      212
      213
      214
      215
      216
      217
      218
      219
      220
      221
      222
      223
      224
      225
      226
      227
      228
      229
      230
      231
      232
      233
      234
      235
      236
      237
      238
      239
      240
      241
      242
      243
      244
      245
      246
      247
      248
      249
      250
      251
      252
      253
      254
      255
      256
      257
      258
      259
      260
      261
      262
      263
      264
      265
      266
      267
      268
      269
      270
      271
      272
      273
      274
      275
      276
      277
      278
      279
      280
      281
      282
      283
      284
      285
      286
      287
      288
      289
      290
      291
      292
      293
      294
      295
      296
      297
      298
      299
      300
      301
      302
      303
      304
      305
      306
      307
      308
      309
      310
      311
      312
      313
      314
      315
      316
      317
      318
      319
      320
      321
      322
      323
      324
      325
      326
      327
      328
      329
      330
      331
      332
      333
      334
      335
      336
      337
      338
      339
      340
      341
      342
      343
      344
      345
      346
      347
      348
      349
      350
      351
      352
      353
      354
      355
      356
      357
      358
      359
      360
      361
      362
      363
      364
      365
      366
      367
      368
      369
      370
      371
      372
      373
      374
      375
      376
      377
      378
      379
      380
      381
      382
      383
      384
      385
      386
      387
      388
      389
      390
      391
      392
      393
      394
      395
      396
      397
      398
      399
      400
      401
      402
      403
      404
      405
      406
      407
      408
      409
      410
      411
      412
      413
      414
      415
      416
      417
      418
      419
      420
      421
      422
      423
      424
      425
      426
      427
      428
      429
      430
      431
      432
      433
      434
      435
      436
      437
      438
      439
      440
      441
      442
      443
      444
      445
      446
      447
      448
      449
      450
      451
      452
      453
      454
      455
      456
      457
      458
      459
      460
      461
      462
      463
      464
      465
      466
      467
      468
      469
      470
      471
      472
      473
      474
      475
      476
      477
      478
      479
      480
      481
      482
      483
      484
      485
      486
      487
      488
      489
      490
      491
      492
      493
      494
      495
      496
      497
      498
      499
      500
      501
      502
      503
      504
      505
      506
      507
      508
      509
      510
      511
      512
      513
      514
      515
      516
      517
      518
      519
      520
      521
      522
      523
      524
      525
      526
      527
      528
      529
      530
      531
      532
      533
      534
      535
      536
      537
      538
      539
      540
      541
      542
      543
      544
      545
      546
      547
      548
      549
      550
      551
      552
      553
      554
      555
      556
      557
      558
      559
      560
      561
      562
      563
      564
      565
      566
      567
      568
      569
      570
      571
      572
      573
      574
      575
      576
      577
      578
      579
      580
      581
      582
      583
      584
      585
      586
      587
      588
      589
      590
      591
      592
      593
      594
      595
      596
      597
      598
      599
      600
      601
      602
      603
      604
      605
      606
      607
      608
      609
      610
      611
      612
      613
      614
      615
      616
      617
      618
      619
      620
      621
      622
      623
      624
      625
      626
      627
      628
      629
      630
      631
      632
      633
      634
      635
      636
      637
      638
      639
      640
      641
      642
      643
      644
      645
      646
      647
      648
      649
      650
      651
      652
      653
      654
      655
      656
      657
      658
      659
      660
      661
      662
      663
      664
      665
      666
      667
      668
      669
      670
      671
      672
      673
      674
      675
      676
      677
      678
      679
      680
      681
      682
      683
      684
      685
      686
      687
      688
      689
      690
      691
      692
      693
      694
      695
      696
      697
      698
      699
      700
      701
      702
      703
      704
      705
      706
      707
      708
      709
      710
      711
      712
      713
      714
      715
      716
      717
      718
      719
      720
      721
      722
      723
      724
      725
      726
      727
      728
      729
      730
      731
      732
      733
      734
      735
      736
      737
      738
      739
      740
      741
      742
      743
      744
      745
      746
      747
      748
      749
      750
      751
      752
      753
      754
      755
      756
      757
      758
      759
      760
      761
      762
      763
      764
      765
      766
      767
      768
      769
      770
      771
      772
      773
      774
      775
      776
      777
      778
      779
      780
      781
      782
      783
      784
      785
      786
      787
      788
      789
      790
      791
      792
      793
      794
      795
      796
      797
      798
      799
      800
      801
      802
      803
      804
      805
      806
      807
      808
      809
      810
      811
      812
      813
      814
      815
      816
      817
      818
      819
      820
      821
      822
      823
      824
      825
      826
      827
      828
      829
      830
      831
      832
      833
      834
      835
      836
      837
      838
      839
      840
      841
      842
      843
      844
      845
      846
      847
      848
      849
      850
      851
      852
      853
      854
      855
      856
      857
      858
      859
      860
      861
      862
      863
      864
      865
      866
      867
      868
      869
      870
      871
      872
      873
      874
      875
      876
      877
      878
      879
      880
      881
      882
      883
      884
      885
      886
      887
      888
      889
      890
      891
      892
      893
      894
      895
      896
      897
      898
      899
      900
      901
      902
      903
      904
      905
      906
      907
      908
      909
      910
      911
      912
      913
      914
      915
      916
      917
      918
      919
      920
      921
      922
      923
      924
      925
      926
      927
      928
      929
      930
      931
      932
      933
      934
      935
      936
      937
      938
      939
      940
      941
      942
      943
      944
      945
      946
      947
      948
      949
      950
      951
      952
      953
      954
      955
      956
      957
      958
      959
      960
      961
      962
      963
      964
      965
      966
      967
      968
      969
      970
      971
      972
      973
      974
      975
      976
      977
      978
      979
      980
      981
      982
      983
      984
      985
      986
      987
      988
      989
      990
      991
      992
      993
      994
      995
      996
      997
      998
      999
     1000
     1001
     1002
     1003
     1004
     1005
     1006
     1007
     1008
     1009
     1010
     1011
     1012
     1013
     1014
     1015
     1016
     1017
     1018
     1019
     1020
     1021
     1022
     1023
     1024
     1025
     1026
     1027
     1028
     1029
     1030
     1031
     1032
     1033
     1034
     1035
     1036
     1037
     1038
     1039
     1040
     1041
     1042
     1043
     1044
     1045
     1046
     1047
     1048
     1049
     1050
     1051
     1052
     1053
     1054
     1055
     1056
     1057
     1058
     1059
     1060
     1061
     1062
     1063
     1064
     1065
     1066
     1067
     1068
     1069
     1070
     1071
     1072
     1073
     1074
     1075
     1076
     1077
     1078
     1079
     1080
     1081
     1082
     1083
     1084
     1085
     1086
     1087
     1088
     1089
     1090
     1091
     1092
     1093
     1094
     1095
     1096
     1097
     1098
     1099
     1100
     1101
     1102
     1103
     1104
     1105
     1106
     1107
     1108
     1109
     1110
     1111
     1112
     1113
     1114
     1115
     1116
     1117
     1118
     1119
     1120
     1121
     1122
     1123
     1124
     1125
     1126
     1127
     1128
     1129
     1130
     1131
     1132
     1133
     1134
     1135
     1136
     1137
     1138
     1139
     1140
     1141
     1142
     1143
     1144
     1145
     1146
     1147
     1148
     1149
     1150
     1151
     1152
     1153
     1154
     1155
     1156
     1157
     1158
     1159
     1160
     1161
     1162
     1163
     1164
     1165
     1166
     1167
     1168
     1169
     1170
     1171
     1172
     1173
     1174
     1175
     1176
     1177
     1178
     1179
     1180
     1181
     1182
     1183
     1184
     1185
     1186
     1187
     1188
     1189
     1190
     1191
     1192
     1193
     1194
     1195
     1196
     1197
     1198
     1199
     1200
     1201
     1202
     1203
     1204
     1205
     1206
     1207
     1208
     1209
     1210
     1211
     1212
     1213
     1214
     1215
     1216
     1217
     1218
     1219
     1220
     1221
     1222
     1223
     1224
     1225
     1226
     1227
     1228
     1229
     1230
     1231
     1232
     1233
     1234
     1235
     1236
     1237
     1238
     1239
     1240
     1241
     1242
     1243
     1244
     1245
     1246
     1247
     1248
     1249
     1250
     1251
     1252
     1253
     1254
     1255
     1256
     1257
     1258
     1259
     1260
     1261
     1262
     1263
     1264
     1265
     1266
     1267
     1268
     1269
     1270
     1271
     1272
     1273
     1274
     1275
     1276
     1277
     1278
     1279
     1280
     1281
     1282
     1283
     1284
     1285
     1286
     1287
     1288
     1289
     1290
     1291
     1292
     1293
     1294
     1295
     1296
     1297
     1298
     1299
     1300
     1301
     1302
     1303
     1304
     1305
     1306
     1307
     1308
     1309
     1310
     1311
     1312
     1313
     1314
     1315
     1316
     1317
     1318
     1319
     1320
     1321
     1322
     1323
     1324
     1325
     1326
     1327
     1328
     1329
     1330
     1331
     1332
     1333
     1334
     1335
     1336
     1337
     1338
     1339
     1340
     1341
     1342
     1343
     1344
     1345
     1346
     1347
     1348
     1349
     1350
     1351
     1352
     1353
     1354
     1355
     1356
     1357
     1358
     1359
     1360
     1361
     1362
     1363
     1364
     1365
     1366
     1367
     1368
     1369
     1370
     1371
     1372
     1373
     1374
     1375
     1376
     1377
     1378
     1379
     1380
     1381
     1382
     1383
     1384
     1385
     1386
     1387
     1388
     1389
     1390
     1391
     1392
     1393
     1394
     1395
     1396
     1397
     1398
     1399
     1400
     1401
     1402
     1403
     1404
     1405
     1406
     1407
     1408
     1409
     1410
     1411
     1412
     1413
     1414
     1415
     1416
     1417
     1418
     1419
     1420
     1421
     1422
     1423
     1424
     1425
     1426
     1427
     1428
     1429
     1430
     1431
     1432
     1433
     1434
     1435
     1436
     1437
     1438
     1439
     1440
     1441
     1442
     1443
     1444
     1445
     1446
     1447
     1448
     1449
     1450
     1451
     1452
     1453
     1454
     1455
     1456
     1457
     1458
     1459
     1460
     1461
/*
 *   Copyright (c) 2012, Michael Lehn
 *
 *   All rights reserved.
 *
 *   Redistribution and use in source and binary forms, with or without
 *   modification, are permitted provided that the following conditions
 *   are met:
 *
 *   1) Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *   2) Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in
 *      the documentation and/or other materials provided with the
 *      distribution.
 *   3) Neither the name of the FLENS development group nor the names of
 *      its contributors may be used to endorse or promote products derived
 *      from this software without specific prior written permission.
 *
 *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/* Based on
 *
       SUBROUTINE DGESVJ( JOBA, JOBU, JOBV, M, N, A, LDA, SVA, MV, V,
      $                   LDV, WORK, LWORK, INFO )
 *
 *  -- LAPACK routine (version 3.3.1)                                  --
 *
 *  -- Contributed by Zlatko Drmac of the University of Zagreb and     --
 *  -- Kresimir Veselic of the Fernuniversitaet Hagen                  --
 *  -- April 2011                                                      --
 *
 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
 *
 * This routine is also part of SIGMA (version 1.23, October 23. 2008.)
 * SIGMA is a library of algorithms for highly accurate algorithms for
 * computation of SVD, PSVD, QSVD, (H,K)-SVD, and for solution of the
 * eigenvalue problems Hx = lambda M x, H M x = lambda x with H, M > 0.
 *
 */

#ifndef FLENS_LAPACK_GE_SVJ_TCC
#define FLENS_LAPACK_GE_SVJ_TCC 1

#include <flens/blas/blas.h>
#include <flens/lapack/lapack.h>

namespace flens { namespace lapack {

//== generic lapack implementation =============================================

namespace generic {

template <typename MA, typename VSVA, typename MV, typename VWORK>
typename GeMatrix<MA>::IndexType
svj_impl(SVJ::TypeA                typeA,
         SVJ::JobU                 jobU,
         SVJ::JobV                 jobV,
         GeMatrix<MA>              &A,
         DenseVector<VSVA>         &sva,
         GeMatrix<MV>              &V,
         DenseVector<VWORK>        &work)
{
    using std::abs;
    using std::max;
    using std::min;
    using flens::pow;
    using std::sqrt;
    using std::swap;

    typedef typename GeMatrix<MA>::ElementType  ElementType;
    typedef typename GeMatrix<MA>::IndexType    IndexType;

    const ElementType  Zero(0), Half(0.5), One(1);
    const IndexType    nSweep = 30;

    const Underscore<IndexType>  _;

    ElementType fastr_data[5];
    DenseVectorView<ElementType>
        fastr  = typename DenseVectorView<ElementType>::Engine(5, fastr_data);

    const IndexType  m     = A.numRows();
    const IndexType  n     = A.numCols();
    const IndexType  mv    = V.numRows();
    const IndexType  lWork = work.length();

    const bool lower    = (typeA==SVJ::Lower);
    const bool upper    = (typeA==SVJ::Upper);
    const bool lhsVec   = (jobU==SVJ::ComputeU);
    const bool controlU = (jobU==SVJ::ControlU);
    const bool applyV   = (jobV==SVJ::ApplyV);
    const bool rhsVec   = (jobV==SVJ::ComputeV) || applyV;

    IndexType  info = 0;
//
//#:) Quick return for void matrix
//
    if ((m==0) || (n==0)) {
        return info;
    }
//
//  Set numerical parameters
//  The stopping criterion for Jacobi rotations is
//
//  max_{i<>j}|A(:,i)^T * A(:,j)|/(||A(:,i)||*||A(:,j)||) < CTOL*EPS
//
//  where EPS is the round-off and CTOL is defined as follows:
//
    ElementType  cTol;
    if (controlU) {
//      ... user controlled
        cTol = work(1);
    } else {
//      ... default
        if (lhsVec || rhsVec) {
            cTol = sqrt(ElementType(m));
        } else {
            cTol = ElementType(m);
        }
    }
//    ... and the machine dependent parameters are
//[!]  (Make sure that DLAMCH() works properly on the target machine.)
//
    const ElementType eps = lamch<ElementType>(Eps);
    const ElementType rootEps = sqrt(eps);
    const ElementType safeMin = lamch<ElementType>(SafeMin);
    const ElementType rootSafeMin = sqrt(safeMin);
    const ElementType small = safeMin / eps;
    const ElementType big = lamch<ElementType>(OverflowThreshold);
//  const ElementType big = One / safeMin;
    const ElementType rootBig = One / rootSafeMin;
    const ElementType bigTheta = One / rootEps;

    const ElementType tol = cTol*eps;
    const ElementType rootTol = sqrt(tol);

    if (ElementType(m)*eps>=One) {
//      we return -4 to keep it compatible with the LAPACK implementation
        return -4;
    }
//
//    Initialize the right singular vector matrix.
//
    if (rhsVec && (!applyV)) {
        V         = Zero;
        V.diag(0) = One;
    }
//
//  Initialize SVA( 1:N ) = ( ||A e_i||_2, i = 1:N )
//(!) If necessary, scale A to protect the largest singular value
//  from overflow. It is possible that saving the largest singular
//  value destroys the information about the small ones.
//  This initial scaling is almost minimal in the sense that the
//  goal is to make sure that no column norm overflows, and that
//  DSQRT(N)*max_i SVA(i) does not overflow. If INFinite entries
//  in A are detected, the procedure returns with INFO=-6.
//
    ElementType skl = One / sqrt(ElementType(m)*ElementType(n));
    bool noScale = true;
    bool goScale = true;

    ElementType aapp, aaqq, tmp;

    if (lower) {
//      the input matrix is M-by-N lower triangular (trapezoidal)
        for (IndexType p=1; p<=n; ++p) {
            aapp = Zero;
            aaqq = One;
            lassq(A(_(p,m),p), aapp, aaqq);
            if (aapp>big) {
                return -6;
            }
            aaqq = sqrt(aaqq);
            if ((aapp<(big/aaqq)) && noScale) {
                sva(p) = aapp*aaqq;
            } else {
                noScalefalse;
                sva(p) = aapp*(aaqq*skl);
                if (goScale) {
                    goScalefalse;
                    sva(_(1,p-1)) *= skl;
                }
            }
        }
    } else if (upper) {
//      the input matrix is M-by-N upper triangular (trapezoidal)
        for (IndexType p=1; p<=n; ++p) {
            aapp = Zero;
            aaqq = One;
            lassq(A(_(1,p), p), aapp, aaqq);
            if (aapp>big) {
                return -6;
            }
            aaqq = sqrt(aaqq);
            if ((aapp<(big/aaqq)) && noScale) {
                sva(p) = aapp*aaqq;
            } else {
                noScalefalse;
                sva(p) = aapp*(aaqq*skl);
                if (goScale) {
                    goScalefalse;
                    sva(_(1,p-1)) *= skl;
                }
            }
        }
    } else {
//      the input matrix is M-by-N general dense
        for (IndexType p=1; p<=n; ++p) {
            aapp = Zero;
            aaqq = One;
            lassq(A(_,p), aapp, aaqq);
            if (aapp>big) {
                return -6;
            }
            aaqq = sqrt(aaqq);
            if ((aapp<(big/aaqq)) && noScale) {
                sva(p) = aapp*aaqq;
            } else {
                noScalefalse;
                sva(p) = aapp*(aaqq*skl);
                if (goScale) {
                    goScalefalse;
                    sva(_(1,p-1)) *= skl;
                }
            }
        }
    }

    if (noScale) {
        skl = One;
    }
//
//  Move the smaller part of the spectrum from the underflow threshold
//(!) Start by determining the position of the nonzero entries of the
//  array SVA() relative to ( SFMIN, BIG ).
//
    aapp = Zero;
    aaqq = big;
    for (IndexType p=1; p<=n; ++p) {
        if (sva(p)!=Zero) {
            aaqq = min(aaqq,sva(p));
        }
        aapp = max(aapp,sva(p));
    }
//
//#:) Quick return for zero matrix
//
    if (aapp==Zero) {
        if (lhsVec) {
            A = Zero;
            A.diag(0) = One;
        }
        work(1)      = One;
        work(_(2,6)) = Zero;
        return info;
    }
//
//#:) Quick return for one-column matrix
//
    if (n==1) {
        if (lhsVec) {
            lascl(LASCL::FullMatrix00, sva(1), skl, A);
        }
        work(1) = One / skl;
        if (sva(1)>=safeMin) {
            work(2) = One;
        } else {
            work(2) = Zero;
        }
        work(_(3,6)) = Zero;
        return info;
    }
//
//  Protect small singular values from underflow, and try to
//  avoid underflows/overflows in computing Jacobi rotations.
//
    ElementType cs, sn;

    sn = sqrt(safeMin/eps);
    tmp = sqrt(big/ElementType(n));
    if ((aapp<=sn) || (aaqq>=tmp) || (sn<=aaqq && aapp<=tmp)) {
        tmp = min(big, tmp/aapp);
//      aaqq  = aaqq*tmp
//      aapp  = aapp*tmp
    } else if ((aaqq<=sn) && (aapp<=tmp)) {
        tmp = min(sn/aaqq, big/(aapp*sqrt(ElementType(n))));
//      aaqq  = aaqq*tmp
//      aapp  = aapp*tmp
    } else if ((aaqq>=sn) && (aapp>=tmp)) {
        tmp = max(sn/aaqq, tmp/aapp);
//      aaqq  = aaqq*tmp
//      aapp  = aapp*tmp
    } else if ((aaqq<=sn) && (aapp>=tmp)) {
        tmp = min(sn/aaqq, big/(sqrt(ElementType(n))*aapp));
//      aaqq  = aaqq*tmp
//      aapp  = aapp*tmp
    } else {
        tmp = One;
    }
//
//  Scale, if necessary
//
    if (tmp!=One) {
        lascl(LASCL::FullMatrix00, One, tmp, sva);
    }
    skl *= tmp;
    if (skl!=One) {
        if (upper) {
            lascl(LASCL::UpperTriangular00, One, skl, A);
        } else if (lower) {
            lascl(LASCL::LowerTriangular00, One, skl, A);
        } else {
            lascl(LASCL::FullMatrix00, One, skl, A);
        }
        skl = One / skl;
    }
//
//  Row-cyclic Jacobi SVD algorithm with column pivoting
//
    const IndexType emptsw = n*(n-1)/2;
    IndexType notRot = 0;
    fastr(1) = Zero;
//
//  A is represented in factored form A = A * diag(WORK), where diag(WORK)
//  is initialized to identity. WORK is updated during fast scaled
//  rotations.
//
    work(_(1,n)) = One;
//
//
    IndexType swBand = 3;
//[TP] SWBAND is a tuning parameter [TP]. It is meaningful and effective
//  if DGESVJ is used as a computational routine in the preconditioned
//  Jacobi SVD algorithm DGESVJ. For sweeps i=1:SWBAND the procedure
//  works on pivots inside a band-like region around the diagonal.
//  The boundaries are determined dynamically, based on the number of
//  pivots above a threshold.
//
    const IndexType kbl = min(IndexType(8),n);
//[TP] KBL is a tuning parameter that defines the tile size in the
//  tiling of the p-q loops of pivot pairs. In general, an optimal
//  value of KBL depends on the matrix dimensions and on the
//  parameters of the computer's memory.
//
    IndexType nbl = n / kbl;
    if (nbl*kbl!=n) {
        ++nbl;
    }

    const IndexType blSkip = pow(kbl2);
//[TP] BLKSKIP is a tuning parameter that depends on SWBAND and KBL.
//
    const IndexType rowSkip = min(IndexType(5), kbl);
//[TP] ROWSKIP is a tuning parameter.
//
    const IndexType lkAhead = 1;
//[TP] LKAHEAD is a tuning parameter.
//
//  Quasi block transformations, using the lower (upper) triangular
//  structure of the input matrix. The quasi-block-cycling usually
//  invokes cubic convergence. Big part of this cycle is done inside
//  canonical subspaces of dimensions less than M.
//
    if ((lower || upper) && (n>max(IndexType(64), 4*kbl))) {
//[TP]  The number of partition levels and the actual partition are
//      tuning parameters.
        const IndexType n4 = n4;
        const IndexType n2 = n2;
        const IndexType n34 = 3*n4;
        const IndexType q = (applyV) ? 0 : 1;
        const IndexType qm = (applyV) ? mv0;

        auto _work = work(_(n+1,lWork));

        if (lower) {
//
//          This works very well on lower triangular matrices, in particular
//          in the framework of the preconditioned Jacobi SVD (xGEJSV).
//          The idea is simple:
//          [+ 0 0 0]   Note that Jacobi transformations of [0 0]
//          [+ + 0 0]                                       [0 0]
//          [+ + x 0]   actually work on [x 0]              [x 0]
//          [+ + x x]                    [x x].             [x x]
//
            auto A1 = A(_(    1,m),_(    1, n4));
            auto A2 = A(_( n4+1,m),_( n4+1, n2));
            auto A3 = A(_( n2+1,m),_( n2+1,n34));
            auto A4 = A(_(n34+1,m),_(n34+1,  n));

            auto A12 = A(_(   1,m),_(   1,n2));
            auto A34 = A(_(n2+1,m),_(n2+1, n));

            auto V1 = V(_(      1, n4*q+qm),_(    1,n4));
            auto V2 = V(_( n4*q+1, n2*q+qm),_( n4+1,n2));
            auto V3 = V(_( n2*q+1,n34*q+qm),_( n2+1,n34));
            auto V4 = V(_(n34*q+1, mv*q+qm),_(n34+1,n));

            auto V12 = V(_(      1,n2*q+qm),_(   1,n2));
            auto V34 = V(_( n2*q+1,mv*q+qm),_(n2+1,n));

            auto d1 = work(_(    1, n4));
            auto d2 = work(_( n4+1, n2));
            auto d3 = work(_( n2+1,n34));
            auto d4 = work(_(n34+1,  n));

            auto d12 = work(_(    1,n2));
            auto d34 = work(_( n2+1, n));

            auto sva1 = sva(_(    1, n4));
            auto sva2 = sva(_( n4+1, n2));
            auto sva3 = sva(_( n2+1,n34));
            auto sva4 = sva(_(n34+1,  n));

            auto sva12 = sva(_(   1,n2));
            auto sva34 = sva(_(n2+1, n));

            svj0(jobV, A4, d4, sva4, V4, eps, safeMin, tol2, _work);
            svj0(jobV, A3, d3, sva3, V3, eps, safeMin, tol2, _work);
            svj1(jobV, n4, A34, d34, sva34, V34, eps, safeMin, tol1, _work);
            svj0(jobV, A2, d2, sva2, V2, eps, safeMin, tol1, _work);
            svj0(jobV, A1, d1, sva1, V1, eps, safeMin, tol1, _work);
            svj1(jobV, n4, A12, d12, sva12, V12, eps, safeMin, tol1, _work);

        } else if (upper) {

            auto A1 = A(_(1,   n4),_(    1,   n4));
            auto A2 = A(_(1,   n2),_( n4+1,n4+n4));
            auto A3 = A(_(1,n2+n4),_( n2+1,n2+n4));

            auto A12 = A(_(1,n2),_(1,n2));

            auto V1 = V(_(      1,     n4*q+qm),_(    1,   n4));
            auto V2 = V(_( n4*q+1,(n4+n4)*q+qm),_( n4+1,n4+n4));
            auto V3 = V(_( n2*q+1,(n2+n4)*q+qm),_( n2+1,n2+n4));

            auto V12 = V(_(1,n2*q+qm),_(1,n2));

            auto d1 = work(_(    1,   n4));
            auto d2 = work(_( n4+1,n4+n4));
            auto d3 = work(_( n2+1,n2+n4));

            auto d12 = work(_(1,n2));

            auto sva1 = sva(_(    1,   n4));
            auto sva2 = sva(_( n4+1,n4+n4));
            auto sva3 = sva(_( n2+1,n2+n4));

            auto sva12 = sva(_(1,n2));

            svj0(jobV, A1, d1, sva1, V1, eps, safeMin, tol2, _work);
            svj0(jobV, A2, d2, sva2, V2, eps, safeMin, tol1, _work);
            svj1(jobV, n4, A12, d12, sva12, V12, eps, safeMin, tol1, _work);
            svj0(jobV, A3, d3, sva3, V3, eps, safeMin, tol1, _work);

        }

    }
//
//  .. Row-cyclic pivot strategy with de Rijk's pivoting ..
//
    ElementType max_aapq, aapq, aapp0, aqoap, apoaq;
    ElementType max_sinj;
    ElementType theta, thetaSign, t;

    IndexType   i, iswRot, pSkipped, ibr, igl, jgl, ir1, p, q, jbc, ijblsk;

    bool        converged = false;
    bool        rotOk;

    for (i=1; i<=nSweep; ++i) {
//
//  .. go go go ...
//
       max_aapq = Zero;
       max_sinj = Zero;

       iswRot   = 0;
       pSkipped0;

       notRot   = 0;
//
//     Each sweep is unrolled using KBL-by-KBL tiles over the pivot pairs
//     1 <= p < q <= N. This is the first step toward a blocked implementation
//     of the rotations. New implementation, based on block transformations,
//     is under development.
//
       for (ibr=1; ibr<=nbl; ++ibr) {

          igl = (ibr-1)*kbl1;

          for (ir1=0; ir1<=min(lkAhead,nbl-ibr); ++ir1) {

             igl += ir1*kbl;

             for (p=igl; p<=min(igl+kbl-1,n-1); ++p) {
//
//    .. de Rijk's pivoting
//
                q = blas::iamax(sva(_(p,n))) + p1;
                if (p!=q) {
                    blas::swap(A(_,p),A(_,q));
                    if (rhsVec) {
                        blas::swap(V(_,p),V(_,q));
                    }
                    swap(sva(p),sva(q));
                    swap(work(p),work(q));
                }

                if (ir1==0) {
//
//     Column norms are periodically updated by explicit
//     norm computation.
//     Caveat:
//     Unfortunately, some BLAS implementations compute DNRM2(M,A(1,p),1)
//     as DSQRT(DDOT(M,A(1,p),1,A(1,p),1)), which may cause the result to
//     overflow for ||A(:,p)||_2 > DSQRT(overflow_threshold), and to
//     underflow for ||A(:,p)||_2 < DSQRT(underflow_threshold).
//     Hence, DNRM2 cannot be trusted, not even in the case when
//     the true norm is far from the under(over)flow boundaries.
//     If properly implemented DNRM2 is available, the IF-THEN-ELSE
//     below should read "AAPP = DNRM2( M, A(1,p), 1 ) * WORK(p)".
//

                   if ((sva(p)<rootBig) && (sva(p)>rootSafeMin)) {
                      sva(p) = blas::nrm2(A(_,p)) * work(p);
                   } else {
                       tmp = Zero;
                       aapp = One;
                       lassq(A(_,p), tmp, aapp);
                       sva(p) = tmp * sqrt(aapp) * work(p);
                   }
                   aapp = sva(p);
                } else {
                   aapp = sva(p);
                }

                if (aapp>Zero) {

                   pSkipped0;

                   for (q=p+1; q<=min(igl+kbl-1,n); ++q) {

                      aaqq = sva(q);

                      if (aaqq>Zero) {

                         aapp0 = aapp;
                         if (aaqq>=One) {
                            rotOk = (small*aapp<=aaqq);
                            if (aapp<big/aaqq) {
                               aapq = (A(_,p)*A(_,q)*work(p)*work(q)/aaqq)
                                    / aapp;
                            } else {
                               auto _work = work(_(n+1,n+m));

                               _work = A(_,p);
                               lascl(LASCL::FullMatrix00,
                                     aapp, work(p), _work);
                               aapq = _work*A(_,q)*work(q)/aaqq;
                            }
                         } else {
                            rotOk = (aapp<=aaqq/small);
                            if (aapp>(small/aaqq)) {
                                aapq = (A(_,p)*A(_,q)*work(p)*work(q)/aaqq)
                                     / aapp;
                            } else {
                               auto _work = work(_(n+1,n+m));

                               _work = A(_,q);
                               lascl(LASCL::FullMatrix00,
                                     aaqq, work(q), _work);
                               aapq = _work*A(_,p)*work(p)/aapp;
                            }
                         }

                         max_aapq = max(max_aapq, abs(aapq));
//
//     TO rotate or NOT to rotate, THAT is the question ...
//
                         if (abs(aapq)>tol) {
//
//        .. rotate
//[RTD]    ROTATED = ROTATED + ONE
//
                            if (ir1==0) {
                               notRot0;
                               pSkipped0;
                               ++iswRot;
                            }

                            if (rotOk) {

                               aqoap = aaqq / aapp;
                               apoaq = aapp / aaqq;
                               theta = -Half*abs(aqoap-apoaq)/aapq;

                               if (abs(theta)>bigTheta) {

                                  t = Half / theta;
                                  fastr(3) =  t*work(p) / work(q);
                                  fastr(4) = -t*work(q) / work(p);
                                  blas::rotm(A(_,p), A(_,q), fastr);
                                  if (rhsVec) {
                                      blas::rotm(V(_,p), V(_,q), fastr);
                                  }
                                  sva(q) =aaqq*sqrt(max(Zero,One+t*apoaq*aapq));
                                  aapp *= sqrt(max(Zero, One-t*aqoap*aapq));
                                  max_sinj = max(max_sinj, abs(t));

                               } else {
//
//              .. choose correct signum for THETA and rotate
//
                                  thetaSign = -sign(One,aapq);
                                  t = One
                                    / (theta +thetaSign*sqrt(One+theta*theta));
                                  cs = sqrt(One / (One+t*t));
                                  sn = t*cs;

                                  max_sinj = max(max_sinj, abs(sn));
                                  sva(q) = aaqq
                                          *sqrt(max(Zero, One+t*apoaq*aapq));
                                  aapp *= sqrt(max(Zero, One-t*aqoap*aapq));

                                  apoaq = work(p) / work(q);
                                  aqoap = work(q) / work(p);
                                  if (work(p)>=One) {
                                     if (work(q)>=One) {
                                        fastr(3) =  t*apoaq;
                                        fastr(4) = -t*aqoap;
                                        work(p) *= cs;
                                        work(q) *= cs;
                                        blas::rotm(A(_,p), A(_,q), fastr);
                                        if (rhsVec) {
                                            blas::rotm(V(_,p), V(_,q), fastr);
                                        }
                                     } else {
                                        A(_,p) -= t*aqoap*A(_,q);
                                        A(_,q) += cs*sn*apoaq*A(_,p);
                                        work(p) *= cs;
                                        work(q) /= cs;
                                        if (rhsVec) {
                                           V(_,p) -= t*aqoap*V(_,q);
                                           V(_,q) += cs*sn*apoaq*V(_,p);
                                        }
                                     }
                                  } else {
                                     if (work(q)>=One) {
                                        A(_,q) += t*apoaq*A(_,p);
                                        A(_,p) -= cs*sn*aqoap*A(_,q);
                                        work(p) /= cs;
                                        work(q) *= cs;
                                        if (rhsVec) {
                                           V(_,q) += t*apoaq*V(_,p);
                                           V(_,p) -= cs*sn*aqoap*V(_,q);
                                        }
                                     } else {
                                        if (work(p)>=work(q)) {
                                           A(_,p) -= t*aqoap*A(_,q);
                                           A(_,q) += cs*sn*apoaq*A(_,p);
                                           work(p) *= cs;
                                           work(q) /= cs;
                                           if (rhsVec) {
                                              V(_,p) -= t*aqoap*V(_,q);
                                              V(_,q) += cs*sn*apoaq*V(_,p);
                                           }
                                        } else {
                                           A(_,q) += t*apoaq*A(_,p);
                                           A(_,p) -= cs*sn*aqoap*A(_,q);
                                           work(p) /= cs;
                                           work(q) *= cs;
                                           if (rhsVec) {
                                              V(_,q) += t*apoaq*V(_,p);
                                              V(_,p) -= cs*sn*aqoap*V(_,q);
                                           }
                                        }
                                     }
                                  }
                               }

                            } else {
//             .. have to use modified Gram-Schmidt like transformation
                               auto _work = work(_(n+1,lWork));

                               _work = A(_,p);
                               lascl(LASCL::FullMatrix00,
                                     aapp, One, _work);
                               lascl(LASCL::FullMatrix00,
                                     aaqq, One, A(_,q));
                               tmp = -aapq*work(p)/work(q);
                               A(_,q) += tmp*_work;
                               lascl(LASCL::FullMatrix00,
                                     One, aaqq, A(_,q));
                               sva(q) = aaqq*sqrt(max(Zero, One-aapq*aapq));
                               max_sinj = max(max_sinj, safeMin);
                            }
//        END IF ROTOK THEN ... ELSE
//
//        In the case of cancellation in updating SVA(q), SVA(p)
//        recompute SVA(q), SVA(p).
//
                            if (pow(sva(q)/aaqq,2)<=rootEps) {
                               if ((aaqq<rootBig) && (aaqq>rootSafeMin)) {
                                  sva(q) = blas::nrm2(A(_,q))*work(q);
                               } else {
                                  t = Zero;
                                  aaqq = One;
                                  lassq(A(_,q), t, aaqq);
                                  sva(q) = t*sqrt(aaqq)*work(q);
                               }
                            }
                            if (aapp/aapp0<=rootEps) {
                               if ((aapp<rootBig) && (aapp>rootSafeMin)) {
                                  aapp = blas::nrm2(A(_,p))*work(p);
                               } else {
                                  t = Zero;
                                  aapp = One;
                                  lassq(A(_,p), t, aapp);
                                  aapp = t*sqrt(aapp)*work(p);
                               }
                               sva(p) = aapp;
                            }
//
                         } else {
//     A(:,p) and A(:,q) already numerically orthogonal
                            if (ir1==0) {
                                ++notRot;
                            }
//[RTD]    SKIPPED  = SKIPPED  + 1
                            ++pSkipped;
                         }
                      } else {
//     A(:,q) is zero column
                         if (ir1==0) {
                             ++notRot;
                         }
                         ++pSkipped;
                      }
//
                      if ((i<=swBand) && (pSkipped>rowSkip)) {
                         if (ir1==0) {
                             aapp = -aapp;
                         }
                         notRot0;
                         break;
                      }

                   }
//  END q-LOOP
//
                   sva(p) = aapp;

                } else {
                   sva(p) = aapp;
                   if ((ir1==0) && (aapp==Zero)) {
                       notRot += min(igl+kbl-1,n) - p;
                   }
                }

             }
//  end of the p-loop
//  end of doing the block ( ibr, ibr )
          }
//  end of ir1-loop
//
//... go to the off diagonal blocks
//
          igl = (ibr-1)*kbl1;

          for (jbc=ibr+1; jbc<=nbl; ++jbc) {

             jgl = (jbc-1)*kbl1;
//
//     doing the block at ( ibr, jbc )
//
             ijblsk0;
             for (p=igl; p<=min(igl+kbl-1,n); ++p) {

                aapp = sva(p);
                if (aapp>Zero) {

                   pSkipped0;

                   for (q=jgl; q<=min(jgl+kbl-1,n); ++q) {

                      aaqq = sva(q);
                      if (aaqq>Zero) {
                         aapp0 = aapp;

//
//  .. M x 2 Jacobi SVD ..
//
//     Safe Gram matrix computation
//
                         if (aaqq>=One) {
                            if (aapp>=aaqq) {
                               rotOk = (small*aapp)<=aaqq;
                            } else {
                               rotOk = (small*aaqq)<=aapp;
                            }
                            if (aapp<(big/aaqq)) {
                               aapq = (A(_,p)*A(_,q)*work(p)*work(q)/aaqq)
                                    / aapp;
                            } else {
                               auto _work = work(_(n+1,n+m));

                               _work = A(_,p);
                               lascl(LASCL::FullMatrix00,
                                     aapp, work(p), _work);
                               aapq = _work*A(_,q)*work(q) / aaqq;
                            }
                         } else {
                            if (aapp>=aaqq) {
                               rotOk = aapp<=(aaqq/small);
                            } else {
                               rotOk = aaqq<=(aapp/small);
                            }
                            if (aapp>(small/aaqq)) {
                               aapq = (A(_,p)*A(_,q)*work(p)*work(q)/aaqq)
                                    / aapp;
                            } else {
                               auto _work = work(_(n+1,n+m));

                               _work = A(_,q);
                               lascl(LASCL::FullMatrix00,
                                     aaqq, work(q), _work);
                               aapq = _work*A(_,p)*work(p)/aapp;
                            }
                         }

                         max_aapq = max(max_aapq, abs(aapq));
//
//     TO rotate or NOT to rotate, THAT is the question ...
//
                         if (abs(aapq)>tol) {
                            notRot0;
//[RTD]    ROTATED  = ROTATED + 1
                            pSkipped0;
                            ++iswRot;

                            if (rotOk) {

                               aqoap = aaqq / aapp;
                               apoaq = aapp / aaqq;
                               theta = -Half*abs(aqoap-apoaq)/aapq;
                               if (aaqq>aapp0) {
                                  theta = -theta;
                               }

                               if (abs(theta)>bigTheta) {
                                  t = Half/theta;
                                  fastr(3) =  t*work(p) / work(q);
                                  fastr(4) = -t*work(q) / work(p);
                                  blas::rotm(A(_,p), A(_,q), fastr);
                                  if (rhsVec) {
                                     blas::rotm(V(_,p), V(_,q), fastr);
                                  }
                                  sva(q) = aaqq
                                         * sqrt(max(Zero, One+t*apoaq*aapq));
                                  aapp *= sqrt(max(Zero,One-t*aqoap*aapq));
                                  max_sinj = max(max_sinj, abs(t));
                               } else {
//
//              .. choose correct signum for THETA and rotate
//
                                  thetaSign = -sign(One,aapq);
                                  if (aaqq>aapp0) {
                                      thetaSign = -thetaSign;
                                  }
                                  t = One
                                    / (theta+thetaSign*sqrt(One+theta*theta));
                                  cs = sqrt(One / (One + t*t));
                                  sn = t*cs;
                                  max_sinj = max(max_sinj, abs(sn));
                                  sva(q) = aaqq
                                         * sqrt(max(Zero, One+t*apoaq*aapq));
                                  aapp *= sqrt(max(Zero, One-t*aqoap*aapq));

                                  apoaq = work(p) / work(q);
                                  aqoap = work(q) / work(p);
                                  if (work(p)>=One) {

                                     if (work(q)>=One) {
                                        fastr(3) =  t*apoaq;
                                        fastr(4) = -t*aqoap;
                                        work(p) *= cs;
                                        work(q) *= cs;
                                        blas::rotm(A(_,p), A(_,q), fastr);
                                        if (rhsVec) {
                                            blas::rotm(V(_,p), V(_,q), fastr);
                                        }
                                     } else {
                                        A(_,p) -= t*aqoap*A(_,q);
                                        A(_,q) += cs*sn*apoaq*A(_,p);
                                        if (rhsVec) {
                                           V(_,p) -= t*aqoap*V(_,q);
                                           V(_,q) += cs*sn*apoaq*V(_,p);
                                        }
                                        work(p) *= cs;
                                        work(q) /= cs;
                                     }
                                  } else {
                                     if (work(q)>=One) {
                                        A(_,q) += t*apoaq*A(_,p);
                                        A(_,p) -= cs*sn*aqoap*A(_,q);
                                        if (rhsVec) {
                                           V(_,q) += t*apoaq*V(_,p);
                                           V(_,p) -= cs*sn*aqoap*V(_,q);
                                        }
                                        work(p) /= cs;
                                        work(q) *= cs;
                                     } else {
                                        if (work(p)>=work(q)) {
                                           A(_,p) -= t*aqoap*A(_,q);
                                           A(_,q) += cs*sn*apoaq*A(_,p);
                                           work(p) *= cs;
                                           work(q) /= cs;
                                           if (rhsVec) {
                                              V(_,p) -= t*aqoap*V(_,q);
                                              V(_,q) += cs*sn*apoaq*V(_,p);
                                           }
                                        } else {
                                           A(_,q) += t*apoaq*A(_,p);
                                           A(_,p) -= cs*sn*aqoap*A(_,q);
                                           work(p) /= cs;
                                           work(q) *= cs;
                                           if (rhsVec) {
                                              V(_,q) += t*apoaq*V(_,p);
                                              V(_,p) -= cs*sn*aqoap*V(_,q);
                                           }
                                        }
                                     }
                                  }
                               }

                            } else {
                               auto _work = work(_(n+1,lWork));

                               if (aapp>aaqq) {
                                  _work = A(_,p);
                                  lascl(LASCL::FullMatrix00,
                                        aapp, One, _work);
                                  lascl(LASCL::FullMatrix00,
                                        aaqq, One, A(_,q));
                                  tmp = -aapq*work(p) / work(q);
                                  A(_,q) += tmp*_work;
                                  lascl(LASCL::FullMatrix00,
                                        One, aaqq, A(_,q));
                                  sva(q) = aaqq*sqrt(max(Zero, One-aapq*aapq));
                                  max_sinj = max(max_sinj, safeMin);
                               } else {
                                  _work = A(_,q);
                                  lascl(LASCL::FullMatrix00,
                                        aaqq, One, _work);
                                  lascl(LASCL::FullMatrix00,
                                        aapp, One, A(_,p));
                                  tmp = -aapq*work(q) / work(p);
                                  A(_,p) += tmp * _work;
                                  lascl(LASCL::FullMatrix00,
                                        One, aapp, A(_,p));
                                  sva(p) = aapp*sqrt(max(Zero, One-aapq*aapq));
                                  max_sinj = max(max_sinj, safeMin);
                               }
                            }
//        END IF ROTOK THEN ... ELSE
//
//        In the case of cancellation in updating SVA(q)
//        .. recompute SVA(q)
                            if (pow(sva(q)/aaqq,2)<=rootEps) {
                               if ((aaqq<rootBig) && (aaqq>rootSafeMin)) {
                                  sva(q) = blas::nrm2(A(_,q))*work(q);
                               } else {
                                  t = Zero;
                                  aaqq = One;
                                  lassq(A(_,q), t, aaqq);
                                  sva(q) = t*sqrt(aaqq)*work(q);
                               }
                            }
                            if (pow(aapp/aapp0,2)<=rootEps) {
                               if ((aapp<rootBig) && (aapp>rootSafeMin)) {
                                  aapp = blas::nrm2(A(_,p))*work(p);
                               } else {
                                  t = Zero;
                                  aapp = One;
                                  lassq(A(_,p), t, aapp);
                                  aapp = t*sqrt(aapp)*work(p);
                               }
                               sva(p) = aapp;
                            }
//             end of OK rotation
                         } else {
                            ++notRot;
//[RTD]      SKIPPED  = SKIPPED  + 1
                            ++pSkipped;
                            ++ijblsk;
                         }
                      } else {
                         ++notRot;
                         ++pSkipped;
                         ++ijblsk;
                      }

                      if ((i<=swBand) && (ijblsk>=blSkip)) {
                         sva(p) = aapp;
                         notRot0;
                         goto jbcLoopExit;
                      }
                      if ((i<=swBand) && (pSkipped>rowSkip)) {
                         aapp = -aapp;
                         notRot0;
                         break;
                      }

                   }
//       end of the q-loop

                   sva(p) = aapp;

                } else {

                   if (aapp==Zero) {
                      notRot += min(jgl+kbl-1,n) -jgl1;
                   }
                   if (aapp<Zero) {
                      notRot0;
                   }

                }

             }
//  end of the p-loop
          }
//  end of the jbc-loop
       jbcLoopExit:
//  bailed out of the jbc-loop
          for (p=igl; p<=min(igl+kbl-1,n); ++p) {
             sva(p) = abs(sva(p));
          }
//**
       }
//  end of the ibr-loop
//
//  .. update SVA(N)
       if ((sva(n)<rootBig) && (sva(n)>rootSafeMin)) {
          sva(n) = blas::nrm2(A(_,n))*work(n);
       } else {
          t = Zero;
          aapp = One;
          lassq(A(_,n), t, aapp);
          sva(n) = t*sqrt(aapp)*work(n);
       }
//
//  Additional steering devices
//
       if ((i<swBand) && ((max_aapq<=rootTol) || (iswRot<=n))) {
          swBand = i;
       }

       if (i>swBand+1 && max_aapq<sqrt(ElementType(n))*tol
        && ElementType(n)*max_aapq*max_sinj<tol) {
           convergedtrue;
           break;
       }

       if (notRot>=emptsw) {
           convergedtrue;
           break;
       }

    }
//  end i=1:NSWEEP loop
//
    if (converged) {
//#:) INFO = 0 confirms successful iterations.
        info0;
    } else {
//#:( Reaching this point means that the procedure has not converged.
        info = nSweep1;
    }
//
//  Sort the singular values and find how many are above
//  the underflow threshold.
//
    IndexType n2 = 0;
    IndexType n4 = 0;
    for (IndexType p=1; p<=n-1; ++p) {
        const IndexType q = blas::iamax(sva(_(p,n))) + p1;
        if (p!=q) {
            swap(sva(p), sva(q));
            swap(work(p), work(q));
            blas::swap(A(_,p), A(_,q));
            if (rhsVec) {
                blas::swap(V(_,p), V(_,q));
            }
        }
        if (sva(p)!=Zero) {
            ++n4;
            if (sva(p)*skl>safeMin) {
                ++n2;
            }
        }
    }
    if (sva(n)!=Zero) {
        ++n4;
        if (sva(n)*skl>safeMin) {
            ++n2;
        }
    }
//
//  Normalize the left singular vectors.
//
    if (lhsVec || controlU) {
        for (IndexType p=1; p<=n2; ++p) {
            A(_,p) *= work(p)/sva(p);
        }
    }
//
//  Scale the product of Jacobi rotations (assemble the fast rotations).
//
    if (rhsVec) {
        if (applyV) {
            for (IndexType p=1; p<=n; ++p) {
                V(_,p) *= work(p);
            }
        } else {
            for (IndexType p=1; p<=n; ++p) {
                V(_,p) *= One / blas::nrm2(V(_,p));
            }
        }
    }
//
//  Undo scaling, if necessary (and possible).
    if (((skl>One) && (sva(1)<big/skl)) || ((skl<One) && (sva(n2)>safeMin/skl))) {
        sva *= skl;
        skl = One;
    }
//
    work(1) = skl;
//  The singular values of A are SKL*SVA(1:N). If SKL.NE.ONE
//  then some of the singular values may overflow or underflow and
//  the spectrum is given in this factored representation.
//
    work(2) = ElementType(n4);
//  N4 is the number of computed nonzero singular values of A.
//
    work(3) = ElementType(n2);
//  N2 is the number of singular values of A greater than SFMIN.
//  If N2<N, SVA(N2:N) contains ZEROS and/or denormalized numbers
//  that may carry some information.
//
    work(4) = ElementType(i);
//  i is the index of the last sweep before declaring convergence.
//
    work(5) = max_aapq;
//  MXAAPQ is the largest absolute value of scaled pivots in the
//  last sweep
//
    work(6) = max_sinj;
//  MXSINJ is the largest absolute value of the sines of Jacobi angles
//  in the last sweep
//
    return info;
}

// namespace generic

//== interface for native lapack ===============================================

#ifdef USE_CXXLAPACK

namespace external {

template <typename MA, typename VSVA, typename MV, typename VWORK>
typename GeMatrix<MA>::IndexType
svj_impl(SVJ::TypeA                typeA,
         SVJ::JobU                 jobU,
         SVJ::JobV                 jobV,
         GeMatrix<MA>              &A,
         DenseVector<VSVA>         &sva,
         GeMatrix<MV>              &V,
         DenseVector<VWORK>        &work)
{
    typedef typename GeMatrix<MA>::IndexType  IndexType;

    return cxxlapack::gesvj<IndexType>(getF77Char(typeA),
                                       getF77Char(jobU),
                                       getF77Char(jobV),
                                       A.numRows(),
                                       A.numCols(),
                                       A.data(),
                                       A.leadingDimension(),
                                       sva.data(),
                                       V.numRows(),
                                       V.data(),
                                       V.leadingDimension(),
                                       work.data(),
                                       work.length());
}

// namespace external

#endif // USE_CXXLAPACK

//== public interface ==========================================================
template <typename MA, typename VSVA, typename MV, typename VWORK>
typename GeMatrix<MA>::IndexType
svj_(SVJ::TypeA                typeA,
     SVJ::JobU                 jobU,
     SVJ::JobV                 jobV,
     GeMatrix<MA>              &A,
     DenseVector<VSVA>         &sva,
     GeMatrix<MV>              &V,
     DenseVector<VWORK>        &work)
{
    using std::max;
    using std::min;

    typedef typename GeMatrix<MA>::IndexType    IndexType;

//
//  Test the input parameters
//
#   ifndef NDEBUG
    ASSERT(A.firstRow()==1);
    ASSERT(A.firstCol()==1);

    const IndexType m = A.numRows();
    const IndexType n = A.numCols();

    ASSERT(m>=n);

    ASSERT(sva.firstIndex()==1);
    ASSERT(sva.length()==n);

    ASSERT(V.firstRow()==1);
    ASSERT(V.firstCol()==1);

    if (jobV==SVJ::ComputeV) {
        ASSERT(V.numCols()==n);
        ASSERT(V.numRows()==n);
    }
    if (jobV==SVJ::ApplyV) {
        ASSERT(V.numCols()==n);
    }

    if (work.length()>0) {
        ASSERT(work.length()>=max(IndexType(6),m+n));
    }
#   endif

//
//  Make copies of output arguments
//
#   ifdef CHECK_CXXLAPACK
    typename GeMatrix<MA>::NoView       A_org     = A;
    typename DenseVector<VSVA>::NoView  sva_org   = sva;
    typename GeMatrix<MV>::NoView       V_org     = V;
    typename DenseVector<VWORK>::NoView work_org  = work;
#   endif

//
//  Call implementation
//
    IndexType info = LAPACK_SELECT::svj_impl(typeA, jobU, jobV,
                                             A, sva, V, work);

#   ifdef CHECK_CXXLAPACK
//
//  Make copies of results computed by the generic implementation
//
    typename GeMatrix<MA>::NoView       A_generic     = A;
    typename DenseVector<VSVA>::NoView  sva_generic   = sva;
    typename GeMatrix<MV>::NoView       V_generic     = V;
    typename DenseVector<VWORK>::NoView work_generic  = work;
//
//  restore output arguments
//
    A    = A_org;
    sva  = sva_org;
    V    = V_org;
    work = work_org;
//
//  Compare generic results with results from the native implementation
//
    IndexType _info = external::svj_impl(typeA, jobU, jobV, A, sva, V, work);

    bool failed = false;
    if (! isIdentical(A_generic, A, "A_generic""A")) {
        std::cerr << "CXXLAPACK: A_generic = " << A_generic << std::endl;
        std::cerr << "F77LAPACK: A = " << A << std::endl;
        failed = true;
    }
    if (! isIdentical(sva_generic, sva, "sva_generic""sva")) {
        std::cerr << "CXXLAPACK: sva_generic = " << sva_generic << std::endl;
        std::cerr << "F77LAPACK: sva = " << sva << std::endl;
        failed = true;
    }
    if (! isIdentical(V_generic, V, "V_generic""V")) {
        std::cerr << "CXXLAPACK: V_generic = " << V_generic << std::endl;
        std::cerr << "F77LAPACK: V = " << V << std::endl;
        failed = true;
    }
    if (! isIdentical(work_generic, work, "work_generic""work")) {
        std::cerr << "CXXLAPACK: work_generic = " << work_generic << std::endl;
        std::cerr << "F77LAPACK: work = " << work << std::endl;
        failed = true;
    }
    if (! isIdentical(info, _info, "info""_info")) {
        std::cerr << "CXXLAPACK: info = " << info << std::endl;
        std::cerr << "F77LAPACK: _info = " << _info << std::endl;
        failed = true;
    }

    if (failed) {
        std::cerr << "error in: svj.tcc ("
                  << ", m = " << m
                  << ", n = " << n
                  << ", typeA = " << char(typeA)
                  << ", jobU = " << char(jobU)
                  << ", jobV = " << char(jobV)
                  << ", info = " << info
                  << ") " << std::endl;
        ASSERT(0);
    } else {
        /*
        std::cerr << "passed: svj.tcc ("
                  << ", m = " << m
                  << ", n = " << n
                  << ", typeA = " << char(typeA)
                  << ", jobU = " << char(jobU)
                  << ", jobV = " << char(jobV)
                  << ", info = " << info
                  << ") " << std::endl;
        */
    }
#   endif

    return info;
}

template <typename MA, typename VSVA, typename MV, typename VWORK>
typename GeMatrix<MA>::IndexType
svj(SVJ::TypeA                typeA,
    SVJ::JobU                 jobU,
    SVJ::JobV                 jobV,
    GeMatrix<MA>              &A,
    DenseVector<VSVA>         &sva,
    GeMatrix<MV>              &V,
    DenseVector<VWORK>        &work)
{
#   ifdef CHECK_CXXLAPACK
    typename GeMatrix<MA>::NoView       A_org    = A;
    typename DenseVector<VSVA>::NoView  sva_org  = sva;
    typename GeMatrix<MV>::NoView       V_org    = V;
    typename DenseVector<VSVA>::NoView  work_org = work;

    svj_(SVJ::Lower, jobU, jobV, A, sva, V, work);

    A    = A_org;
    sva  = sva_org;
    V    = V_org;
    work = work_org;

    svj_(SVJ::Upper, jobU, jobV, A, sva, V, work);

    A    = A_org;
    sva  = sva_org;
    V    = V_org;
    work = work_org;
    svj_(SVJ::General, jobU, jobV, A, sva, V, work);

    A    = A_org;
    sva  = sva_org;
    V    = V_org;
    work = work_org;
#   endif

    return svj_(typeA, jobU, jobV, A, sva, V, work);
}


template <typename MA, typename VSVA, typename MV, typename VWORK>
typename GeMatrix<MA>::IndexType
svj(SVJ::JobU                 jobU,
    SVJ::JobV                 jobV,
    GeMatrix<MA>              &A,
    DenseVector<VSVA>         &sva,
    GeMatrix<MV>              &V,
    DenseVector<VWORK>        &work)
{
    return svj(SVJ::General, jobU, jobV, A, sva, V, work);
}

template <typename MA, typename VSVA, typename MV, typename VWORK>
typename TrMatrix<MA>::IndexType
svj(SVJ::JobU                 jobU,
    SVJ::JobV                 jobV,
    TrMatrix<MA>              &A,
    DenseVector<VSVA>         &sva,
    GeMatrix<MV>              &V,
    DenseVector<VWORK>        &work)
{
    SVJ::TypeA  upLo = (A.upLo()==Upper) ? SVJ::Upper : SVJ::Lower;

    return svj(upLo, jobU, jobV, A.general(), sva, V, work);
}

//-- forwarding ----------------------------------------------------------------
template <typename MA, typename VSVA, typename MV, typename VWORK>
typename MA::IndexType
svj(SVJ::TypeA                typeA,
    SVJ::JobU                 jobU,
    SVJ::JobV                 jobV,
    MA                        &&A,
    VSVA                      &&sva,
    MV                        &&V,
    VWORK                     &&work)
{
    typename MA::IndexType info;

    CHECKPOINT_ENTER;
    info = svj(typeA, jobU, jobV, A, sva, V, work);
    CHECKPOINT_LEAVE;

    return info;
}

template <typename MA, typename VSVA, typename MV, typename VWORK>
typename MA::IndexType
svj(SVJ::JobU                 jobU,
    SVJ::JobV                 jobV,
    MA                        &&A,
    VSVA                      &&sva,
    MV                        &&V,
    VWORK                     &&work)
{
    typename MA::IndexType info;

    CHECKPOINT_ENTER;
    info = svj(jobU, jobV, A, sva, V, work);
    CHECKPOINT_LEAVE;

    return info;
}

} } // namespace lapack, flens

#endif // FLENS_LAPACK_GE_SVJ_TCC