1       SUBROUTINE ZQLT02( M, N, K, A, AF, Q, L, LDA, TAU, WORK, LWORK,
  2      $                   RWORK, RESULT )
  3 *
  4 *  -- LAPACK test routine (version 3.1) --
  5 *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
  6 *     November 2006
  7 *
  8 *     .. Scalar Arguments ..
  9       INTEGER            K, LDA, LWORK, M, N
 10 *     ..
 11 *     .. Array Arguments ..
 12       DOUBLE PRECISION   RESULT* ), RWORK( * )
 13       COMPLEX*16         A( LDA, * ), AF( LDA, * ), L( LDA, * ),
 14      $                   Q( LDA, * ), TAU( * ), WORK( LWORK )
 15 *     ..
 16 *
 17 *  Purpose
 18 *  =======
 19 *
 20 *  ZQLT02 tests ZUNGQL, which generates an m-by-n matrix Q with
 21 *  orthonornmal columns that is defined as the product of k elementary
 22 *  reflectors.
 23 *
 24 *  Given the QL factorization of an m-by-n matrix A, ZQLT02 generates
 25 *  the orthogonal matrix Q defined by the factorization of the last k
 26 *  columns of A; it compares L(m-n+1:m,n-k+1:n) with
 27 *  Q(1:m,m-n+1:m)'*A(1:m,n-k+1:n), and checks that the columns of Q are
 28 *  orthonormal.
 29 *
 30 *  Arguments
 31 *  =========
 32 *
 33 *  M       (input) INTEGER
 34 *          The number of rows of the matrix Q to be generated.  M >= 0.
 35 *
 36 *  N       (input) INTEGER
 37 *          The number of columns of the matrix Q to be generated.
 38 *          M >= N >= 0.
 39 *
 40 *  K       (input) INTEGER
 41 *          The number of elementary reflectors whose product defines the
 42 *          matrix Q. N >= K >= 0.
 43 *
 44 *  A       (input) COMPLEX*16 array, dimension (LDA,N)
 45 *          The m-by-n matrix A which was factorized by ZQLT01.
 46 *
 47 *  AF      (input) COMPLEX*16 array, dimension (LDA,N)
 48 *          Details of the QL factorization of A, as returned by ZGEQLF.
 49 *          See ZGEQLF for further details.
 50 *
 51 *  Q       (workspace) COMPLEX*16 array, dimension (LDA,N)
 52 *
 53 *  L       (workspace) COMPLEX*16 array, dimension (LDA,N)
 54 *
 55 *  LDA     (input) INTEGER
 56 *          The leading dimension of the arrays A, AF, Q and L. LDA >= M.
 57 *
 58 *  TAU     (input) COMPLEX*16 array, dimension (N)
 59 *          The scalar factors of the elementary reflectors corresponding
 60 *          to the QL factorization in AF.
 61 *
 62 *  WORK    (workspace) COMPLEX*16 array, dimension (LWORK)
 63 *
 64 *  LWORK   (input) INTEGER
 65 *          The dimension of the array WORK.
 66 *
 67 *  RWORK   (workspace) DOUBLE PRECISION array, dimension (M)
 68 *
 69 *  RESULT  (output) DOUBLE PRECISION array, dimension (2)
 70 *          The test ratios:
 71 *          RESULT(1) = norm( L - Q'*A ) / ( M * norm(A) * EPS )
 72 *          RESULT(2) = norm( I - Q'*Q ) / ( M * EPS )
 73 *
 74 *  =====================================================================
 75 *
 76 *     .. Parameters ..
 77       DOUBLE PRECISION   ZERO, ONE
 78       PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
 79       COMPLEX*16         ROGUE
 80       PARAMETER          ( ROGUE = ( -1.0D+10-1.0D+10 ) )
 81 *     ..
 82 *     .. Local Scalars ..
 83       INTEGER            INFO
 84       DOUBLE PRECISION   ANORM, EPS, RESID
 85 *     ..
 86 *     .. External Functions ..
 87       DOUBLE PRECISION   DLAMCH, ZLANGE, ZLANSY
 88       EXTERNAL           DLAMCH, ZLANGE, ZLANSY
 89 *     ..
 90 *     .. External Subroutines ..
 91       EXTERNAL           ZGEMM, ZHERK, ZLACPY, ZLASET, ZUNGQL
 92 *     ..
 93 *     .. Intrinsic Functions ..
 94       INTRINSIC          DBLEDCMPLXMAX
 95 *     ..
 96 *     .. Scalars in Common ..
 97       CHARACTER*32       SRNAMT
 98 *     ..
 99 *     .. Common blocks ..
100       COMMON             / SRNAMC / SRNAMT
101 *     ..
102 *     .. Executable Statements ..
103 *
104 *     Quick return if possible
105 *
106       IF( M.EQ.0 .OR. N.EQ.0 .OR. K.EQ.0 ) THEN
107          RESULT1 ) = ZERO
108          RESULT2 ) = ZERO
109          RETURN
110       END IF
111 *
112       EPS = DLAMCH( 'Epsilon' )
113 *
114 *     Copy the last k columns of the factorization to the array Q
115 *
116       CALL ZLASET( 'Full', M, N, ROGUE, ROGUE, Q, LDA )
117       IF( K.LT.M )
118      $   CALL ZLACPY( 'Full', M-K, K, AF( 1, N-K+1 ), LDA,
119      $                Q( 1, N-K+1 ), LDA )
120       IF( K.GT.1 )
121      $   CALL ZLACPY( 'Upper', K-1, K-1, AF( M-K+1, N-K+2 ), LDA,
122      $                Q( M-K+1, N-K+2 ), LDA )
123 *
124 *     Generate the last n columns of the matrix Q
125 *
126       SRNAMT = 'ZUNGQL'
127       CALL ZUNGQL( M, N, K, Q, LDA, TAU( N-K+1 ), WORK, LWORK, INFO )
128 *
129 *     Copy L(m-n+1:m,n-k+1:n)
130 *
131       CALL ZLASET( 'Full', N, K, DCMPLX( ZERO ), DCMPLX( ZERO ),
132      $             L( M-N+1, N-K+1 ), LDA )
133       CALL ZLACPY( 'Lower', K, K, AF( M-K+1, N-K+1 ), LDA,
134      $             L( M-K+1, N-K+1 ), LDA )
135 *
136 *     Compute L(m-n+1:m,n-k+1:n) - Q(1:m,m-n+1:m)' * A(1:m,n-k+1:n)
137 *
138       CALL ZGEMM( 'Conjugate transpose''No transpose', N, K, M,
139      $            DCMPLX-ONE ), Q, LDA, A( 1, N-K+1 ), LDA,
140      $            DCMPLX( ONE ), L( M-N+1, N-K+1 ), LDA )
141 *
142 *     Compute norm( L - Q'*A ) / ( M * norm(A) * EPS ) .
143 *
144       ANORM = ZLANGE( '1', M, K, A( 1, N-K+1 ), LDA, RWORK )
145       RESID = ZLANGE( '1', N, K, L( M-N+1, N-K+1 ), LDA, RWORK )
146       IF( ANORM.GT.ZERO ) THEN
147          RESULT1 ) = ( ( RESID / DBLEMAX1, M ) ) ) / ANORM ) / EPS
148       ELSE
149          RESULT1 ) = ZERO
150       END IF
151 *
152 *     Compute I - Q'*Q
153 *
154       CALL ZLASET( 'Full', N, N, DCMPLX( ZERO ), DCMPLX( ONE ), L, LDA )
155       CALL ZHERK( 'Upper''Conjugate transpose', N, M, -ONE, Q, LDA,
156      $            ONE, L, LDA )
157 *
158 *     Compute norm( I - Q'*Q ) / ( M * EPS ) .
159 *
160       RESID = ZLANSY( '1''Upper', N, L, LDA, RWORK )
161 *
162       RESULT2 ) = ( RESID / DBLEMAX1, M ) ) ) / EPS
163 *
164       RETURN
165 *
166 *     End of ZQLT02
167 *
168       END