1 SUBROUTINE DPTTRS( N, NRHS, D, E, B, LDB, INFO )
2 *
3 * -- LAPACK routine (version 3.3.1) --
4 * -- LAPACK is a software package provided by Univ. of Tennessee, --
5 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
6 * -- April 2011 --
7 *
8 * .. Scalar Arguments ..
9 INTEGER INFO, LDB, N, NRHS
10 * ..
11 * .. Array Arguments ..
12 DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
13 * ..
14 *
15 * Purpose
16 * =======
17 *
18 * DPTTRS solves a tridiagonal system of the form
19 * A * X = B
20 * using the L*D*L**T factorization of A computed by DPTTRF. D is a
21 * diagonal matrix specified in the vector D, L is a unit bidiagonal
22 * matrix whose subdiagonal is specified in the vector E, and X and B
23 * are N by NRHS matrices.
24 *
25 * Arguments
26 * =========
27 *
28 * N (input) INTEGER
29 * The order of the tridiagonal matrix A. N >= 0.
30 *
31 * NRHS (input) INTEGER
32 * The number of right hand sides, i.e., the number of columns
33 * of the matrix B. NRHS >= 0.
34 *
35 * D (input) DOUBLE PRECISION array, dimension (N)
36 * The n diagonal elements of the diagonal matrix D from the
37 * L*D*L**T factorization of A.
38 *
39 * E (input) DOUBLE PRECISION array, dimension (N-1)
40 * The (n-1) subdiagonal elements of the unit bidiagonal factor
41 * L from the L*D*L**T factorization of A. E can also be regarded
42 * as the superdiagonal of the unit bidiagonal factor U from the
43 * factorization A = U**T*D*U.
44 *
45 * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
46 * On entry, the right hand side vectors B for the system of
47 * linear equations.
48 * On exit, the solution vectors, X.
49 *
50 * LDB (input) INTEGER
51 * The leading dimension of the array B. LDB >= max(1,N).
52 *
53 * INFO (output) INTEGER
54 * = 0: successful exit
55 * < 0: if INFO = -k, the k-th argument had an illegal value
56 *
57 * =====================================================================
58 *
59 * .. Local Scalars ..
60 INTEGER J, JB, NB
61 * ..
62 * .. External Functions ..
63 INTEGER ILAENV
64 EXTERNAL ILAENV
65 * ..
66 * .. External Subroutines ..
67 EXTERNAL DPTTS2, XERBLA
68 * ..
69 * .. Intrinsic Functions ..
70 INTRINSIC MAX, MIN
71 * ..
72 * .. Executable Statements ..
73 *
74 * Test the input arguments.
75 *
76 INFO = 0
77 IF( N.LT.0 ) THEN
78 INFO = -1
79 ELSE IF( NRHS.LT.0 ) THEN
80 INFO = -2
81 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
82 INFO = -6
83 END IF
84 IF( INFO.NE.0 ) THEN
85 CALL XERBLA( 'DPTTRS', -INFO )
86 RETURN
87 END IF
88 *
89 * Quick return if possible
90 *
91 IF( N.EQ.0 .OR. NRHS.EQ.0 )
92 $ RETURN
93 *
94 * Determine the number of right-hand sides to solve at a time.
95 *
96 IF( NRHS.EQ.1 ) THEN
97 NB = 1
98 ELSE
99 NB = MAX( 1, ILAENV( 1, 'DPTTRS', ' ', N, NRHS, -1, -1 ) )
100 END IF
101 *
102 IF( NB.GE.NRHS ) THEN
103 CALL DPTTS2( N, NRHS, D, E, B, LDB )
104 ELSE
105 DO 10 J = 1, NRHS, NB
106 JB = MIN( NRHS-J+1, NB )
107 CALL DPTTS2( N, JB, D, E, B( 1, J ), LDB )
108 10 CONTINUE
109 END IF
110 *
111 RETURN
112 *
113 * End of DPTTRS
114 *
115 END
2 *
3 * -- LAPACK routine (version 3.3.1) --
4 * -- LAPACK is a software package provided by Univ. of Tennessee, --
5 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
6 * -- April 2011 --
7 *
8 * .. Scalar Arguments ..
9 INTEGER INFO, LDB, N, NRHS
10 * ..
11 * .. Array Arguments ..
12 DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
13 * ..
14 *
15 * Purpose
16 * =======
17 *
18 * DPTTRS solves a tridiagonal system of the form
19 * A * X = B
20 * using the L*D*L**T factorization of A computed by DPTTRF. D is a
21 * diagonal matrix specified in the vector D, L is a unit bidiagonal
22 * matrix whose subdiagonal is specified in the vector E, and X and B
23 * are N by NRHS matrices.
24 *
25 * Arguments
26 * =========
27 *
28 * N (input) INTEGER
29 * The order of the tridiagonal matrix A. N >= 0.
30 *
31 * NRHS (input) INTEGER
32 * The number of right hand sides, i.e., the number of columns
33 * of the matrix B. NRHS >= 0.
34 *
35 * D (input) DOUBLE PRECISION array, dimension (N)
36 * The n diagonal elements of the diagonal matrix D from the
37 * L*D*L**T factorization of A.
38 *
39 * E (input) DOUBLE PRECISION array, dimension (N-1)
40 * The (n-1) subdiagonal elements of the unit bidiagonal factor
41 * L from the L*D*L**T factorization of A. E can also be regarded
42 * as the superdiagonal of the unit bidiagonal factor U from the
43 * factorization A = U**T*D*U.
44 *
45 * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
46 * On entry, the right hand side vectors B for the system of
47 * linear equations.
48 * On exit, the solution vectors, X.
49 *
50 * LDB (input) INTEGER
51 * The leading dimension of the array B. LDB >= max(1,N).
52 *
53 * INFO (output) INTEGER
54 * = 0: successful exit
55 * < 0: if INFO = -k, the k-th argument had an illegal value
56 *
57 * =====================================================================
58 *
59 * .. Local Scalars ..
60 INTEGER J, JB, NB
61 * ..
62 * .. External Functions ..
63 INTEGER ILAENV
64 EXTERNAL ILAENV
65 * ..
66 * .. External Subroutines ..
67 EXTERNAL DPTTS2, XERBLA
68 * ..
69 * .. Intrinsic Functions ..
70 INTRINSIC MAX, MIN
71 * ..
72 * .. Executable Statements ..
73 *
74 * Test the input arguments.
75 *
76 INFO = 0
77 IF( N.LT.0 ) THEN
78 INFO = -1
79 ELSE IF( NRHS.LT.0 ) THEN
80 INFO = -2
81 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
82 INFO = -6
83 END IF
84 IF( INFO.NE.0 ) THEN
85 CALL XERBLA( 'DPTTRS', -INFO )
86 RETURN
87 END IF
88 *
89 * Quick return if possible
90 *
91 IF( N.EQ.0 .OR. NRHS.EQ.0 )
92 $ RETURN
93 *
94 * Determine the number of right-hand sides to solve at a time.
95 *
96 IF( NRHS.EQ.1 ) THEN
97 NB = 1
98 ELSE
99 NB = MAX( 1, ILAENV( 1, 'DPTTRS', ' ', N, NRHS, -1, -1 ) )
100 END IF
101 *
102 IF( NB.GE.NRHS ) THEN
103 CALL DPTTS2( N, NRHS, D, E, B, LDB )
104 ELSE
105 DO 10 J = 1, NRHS, NB
106 JB = MIN( NRHS-J+1, NB )
107 CALL DPTTS2( N, JB, D, E, B( 1, J ), LDB )
108 10 CONTINUE
109 END IF
110 *
111 RETURN
112 *
113 * End of DPTTRS
114 *
115 END