3 * =========== DOCUMENTATION ===========
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
9 *> Download SSYTRS_AA + dependencies
10 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/ssytrs_aa.f">
12 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/ssytrs_aa.f">
14 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/ssytrs_aa.f">
21 * SUBROUTINE SSYTRS_AA( UPLO, N, NRHS, A, LDA, IPIV, B, LDB,
24 * .. Scalar Arguments ..
26 * INTEGER N, NRHS, LDA, LDB, LWORK, INFO
28 * .. Array Arguments ..
30 * REAL A( LDA, * ), B( LDB, * ), WORK( * )
39 *> SSYTRS_AA solves a system of linear equations A*X = B with a real
40 *> symmetric matrix A using the factorization A = U*T*U**T or
41 *> A = L*T*L**T computed by SSYTRF_AA.
49 *> UPLO is CHARACTER*1
50 *> Specifies whether the details of the factorization are stored
51 *> as an upper or lower triangular matrix.
52 *> = 'U': Upper triangular, form is A = U*T*U**T;
53 *> = 'L': Lower triangular, form is A = L*T*L**T.
59 *> The order of the matrix A. N >= 0.
65 *> The number of right hand sides, i.e., the number of columns
66 *> of the matrix B. NRHS >= 0.
71 *> A is REAL array, dimension (LDA,N)
72 *> Details of factors computed by SSYTRF_AA.
78 *> The leading dimension of the array A. LDA >= max(1,N).
83 *> IPIV is INTEGER array, dimension (N)
84 *> Details of the interchanges as computed by SSYTRF_AA.
89 *> B is REAL array, dimension (LDB,NRHS)
90 *> On entry, the right hand side matrix B.
91 *> On exit, the solution matrix X.
97 *> The leading dimension of the array B. LDB >= max(1,N).
102 *> WORK is DOUBLE array, dimension (MAX(1,LWORK))
107 *> LWORK is INTEGER, LWORK >= MAX(1,3*N-2).
112 *> = 0: successful exit
113 *> < 0: if INFO = -i, the i-th argument had an illegal value
119 *> \author Univ. of Tennessee
120 *> \author Univ. of California Berkeley
121 *> \author Univ. of Colorado Denver
124 *> \date December 2016
126 *> \ingroup realSYcomputational
128 * =====================================================================
129 SUBROUTINE SSYTRS_AA( UPLO, N, NRHS, A, LDA, IPIV, B, LDB,
130 $ WORK, LWORK, INFO )
132 * -- LAPACK computational routine (version 3.7.0) --
133 * -- LAPACK is a software package provided by Univ. of Tennessee, --
134 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
139 * .. Scalar Arguments ..
141 INTEGER N, NRHS, LDA, LDB, LWORK, INFO
143 * .. Array Arguments ..
145 REAL A( LDA, * ), B( LDB, * ), WORK( * )
148 * =====================================================================
151 PARAMETER ( ONE = 1.0E+0 )
153 * .. Local Scalars ..
154 LOGICAL LQUERY, UPPER
155 INTEGER K, KP, LWKOPT
157 * .. External Functions ..
161 * .. External Subroutines ..
162 EXTERNAL SGTSV, SSWAP, STRSM, XERBLA
164 * .. Intrinsic Functions ..
167 * .. Executable Statements ..
170 UPPER = LSAME( UPLO, 'U' )
171 LQUERY = ( LWORK.EQ.-1 )
172 IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
174 ELSE IF( N.LT.0 ) THEN
176 ELSE IF( NRHS.LT.0 ) THEN
178 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
180 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
182 ELSE IF( LWORK.LT.MAX( 1, 3*N-2 ) .AND. .NOT.LQUERY ) THEN
186 CALL XERBLA( 'SSYTRS_AA', -INFO )
188 ELSE IF( LQUERY ) THEN
194 * Quick return if possible
196 IF( N.EQ.0 .OR. NRHS.EQ.0 )
201 * Solve A*X = B, where A = U*T*U**T.
209 $ CALL SSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
213 * Compute (U \P**T * B) -> B [ (U \P**T * B) ]
215 CALL STRSM('L', 'U', 'T', 'U', N-1, NRHS, ONE, A( 1, 2 ), LDA,
218 * Compute T \ B -> B [ T \ (U \P**T * B) ]
220 CALL SLACPY( 'F', 1, N, A(1, 1), LDA+1, WORK(N), 1)
222 CALL SLACPY( 'F', 1, N-1, A(1, 2), LDA+1, WORK(1), 1)
223 CALL SLACPY( 'F', 1, N-1, A(1, 2), LDA+1, WORK(2*N), 1)
225 CALL SGTSV(N, NRHS, WORK(1), WORK(N), WORK(2*N), B, LDB,
229 * Compute (U**T \ B) -> B [ U**T \ (T \ (U \P**T * B) ) ]
231 CALL STRSM( 'L', 'U', 'N', 'U', N-1, NRHS, ONE, A( 1, 2 ), LDA,
234 * Pivot, P * B [ P * (U**T \ (T \ (U \P**T * B) )) ]
240 $ CALL SSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
246 * Solve A*X = B, where A = L*T*L**T.
254 $ CALL SSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )
258 * Compute (L \P**T * B) -> B [ (L \P**T * B) ]
260 CALL STRSM( 'L', 'L', 'N', 'U', N-1, NRHS, ONE, A( 2, 1), LDA,
263 * Compute T \ B -> B [ T \ (L \P**T * B) ]
265 CALL SLACPY( 'F', 1, N, A(1, 1), LDA+1, WORK(N), 1)
267 CALL SLACPY( 'F', 1, N-1, A(2, 1), LDA+1, WORK(1), 1)
268 CALL SLACPY( 'F', 1, N-1, A(2, 1), LDA+1, WORK(2*N), 1)
270 CALL SGTSV(N, NRHS, WORK(1), WORK(N), WORK(2*N), B, LDB,
273 * Compute (L**T \ B) -> B [ L**T \ (T \ (L \P**T * B) ) ]
275 CALL STRSM( 'L', 'L', 'T', 'U', N-1, NRHS, ONE, A( 2, 1 ), LDA,
278 * Pivot, P * B [ P * (L**T \ (T \ (L \P**T * B) )) ]
284 $ CALL SSWAP( NRHS, B( K, 1 ), LDB, B( KP, 1 ), LDB )