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First attempt at single precision tyeps * * * corrections to qrupdate single precision routines * * * prefer demotion to single over promotion to double * * * Add single precision support to log2 function * * * Trivial PROJECT file update * * * Cache optimized hermitian/transpose methods * * * Add tests for tranpose/hermitian and ChangeLog entry for new transpose code
author David Bateman <dbateman@free.fr>
date Sun, 27 Apr 2008 22:34:17 +0200
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7788:45f5faba05a2 7789:82be108cc558
1 SUBROUTINE SGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB,
2 $ INFO )
3 *
4 * -- LAPACK routine (version 3.1) --
5 * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
6 * November 2006
7 *
8 * .. Scalar Arguments ..
9 CHARACTER TRANS
10 INTEGER INFO, LDB, N, NRHS
11 * ..
12 * .. Array Arguments ..
13 INTEGER IPIV( * )
14 REAL B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * )
15 * ..
16 *
17 * Purpose
18 * =======
19 *
20 * SGTTRS solves one of the systems of equations
21 * A*X = B or A'*X = B,
22 * with a tridiagonal matrix A using the LU factorization computed
23 * by SGTTRF.
24 *
25 * Arguments
26 * =========
27 *
28 * TRANS (input) CHARACTER*1
29 * Specifies the form of the system of equations.
30 * = 'N': A * X = B (No transpose)
31 * = 'T': A'* X = B (Transpose)
32 * = 'C': A'* X = B (Conjugate transpose = Transpose)
33 *
34 * N (input) INTEGER
35 * The order of the matrix A.
36 *
37 * NRHS (input) INTEGER
38 * The number of right hand sides, i.e., the number of columns
39 * of the matrix B. NRHS >= 0.
40 *
41 * DL (input) REAL array, dimension (N-1)
42 * The (n-1) multipliers that define the matrix L from the
43 * LU factorization of A.
44 *
45 * D (input) REAL array, dimension (N)
46 * The n diagonal elements of the upper triangular matrix U from
47 * the LU factorization of A.
48 *
49 * DU (input) REAL array, dimension (N-1)
50 * The (n-1) elements of the first super-diagonal of U.
51 *
52 * DU2 (input) REAL array, dimension (N-2)
53 * The (n-2) elements of the second super-diagonal of U.
54 *
55 * IPIV (input) INTEGER array, dimension (N)
56 * The pivot indices; for 1 <= i <= n, row i of the matrix was
57 * interchanged with row IPIV(i). IPIV(i) will always be either
58 * i or i+1; IPIV(i) = i indicates a row interchange was not
59 * required.
60 *
61 * B (input/output) REAL array, dimension (LDB,NRHS)
62 * On entry, the matrix of right hand side vectors B.
63 * On exit, B is overwritten by the solution vectors X.
64 *
65 * LDB (input) INTEGER
66 * The leading dimension of the array B. LDB >= max(1,N).
67 *
68 * INFO (output) INTEGER
69 * = 0: successful exit
70 * < 0: if INFO = -i, the i-th argument had an illegal value
71 *
72 * =====================================================================
73 *
74 * .. Local Scalars ..
75 LOGICAL NOTRAN
76 INTEGER ITRANS, J, JB, NB
77 * ..
78 * .. External Functions ..
79 INTEGER ILAENV
80 EXTERNAL ILAENV
81 * ..
82 * .. External Subroutines ..
83 EXTERNAL SGTTS2, XERBLA
84 * ..
85 * .. Intrinsic Functions ..
86 INTRINSIC MAX, MIN
87 * ..
88 * .. Executable Statements ..
89 *
90 INFO = 0
91 NOTRAN = ( TRANS.EQ.'N' .OR. TRANS.EQ.'n' )
92 IF( .NOT.NOTRAN .AND. .NOT.( TRANS.EQ.'T' .OR. TRANS.EQ.
93 $ 't' ) .AND. .NOT.( TRANS.EQ.'C' .OR. TRANS.EQ.'c' ) ) THEN
94 INFO = -1
95 ELSE IF( N.LT.0 ) THEN
96 INFO = -2
97 ELSE IF( NRHS.LT.0 ) THEN
98 INFO = -3
99 ELSE IF( LDB.LT.MAX( N, 1 ) ) THEN
100 INFO = -10
101 END IF
102 IF( INFO.NE.0 ) THEN
103 CALL XERBLA( 'SGTTRS', -INFO )
104 RETURN
105 END IF
106 *
107 * Quick return if possible
108 *
109 IF( N.EQ.0 .OR. NRHS.EQ.0 )
110 $ RETURN
111 *
112 * Decode TRANS
113 *
114 IF( NOTRAN ) THEN
115 ITRANS = 0
116 ELSE
117 ITRANS = 1
118 END IF
119 *
120 * Determine the number of right-hand sides to solve at a time.
121 *
122 IF( NRHS.EQ.1 ) THEN
123 NB = 1
124 ELSE
125 NB = MAX( 1, ILAENV( 1, 'SGTTRS', TRANS, N, NRHS, -1, -1 ) )
126 END IF
127 *
128 IF( NB.GE.NRHS ) THEN
129 CALL SGTTS2( ITRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB )
130 ELSE
131 DO 10 J = 1, NRHS, NB
132 JB = MIN( NRHS-J+1, NB )
133 CALL SGTTS2( ITRANS, N, JB, DL, D, DU, DU2, IPIV, B( 1, J ),
134 $ LDB )
135 10 CONTINUE
136 END IF
137 *
138 * End of SGTTRS
139 *
140 END