LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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◆ dsysv_aa_2stage()

subroutine dsysv_aa_2stage ( character  UPLO,
integer  N,
integer  NRHS,
double precision, dimension( lda, * )  A,
integer  LDA,
double precision, dimension( * )  TB,
integer  LTB,
integer, dimension( * )  IPIV,
integer, dimension( * )  IPIV2,
double precision, dimension( ldb, * )  B,
integer  LDB,
double precision, dimension( * )  WORK,
integer  LWORK,
integer  INFO 
)

DSYSV_AA_2STAGE computes the solution to system of linear equations A * X = B for SY matrices

Download DSYSV_AA_2STAGE + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 DSYSV_AA_2STAGE computes the solution to a real system of
 linear equations
    A * X = B,
 where A is an N-by-N symmetric matrix and X and B are N-by-NRHS
 matrices.

 Aasen's 2-stage algorithm is used to factor A as
    A = U**T * T * U,  if UPLO = 'U', or
    A = L * T * L**T,  if UPLO = 'L',
 where U (or L) is a product of permutation and unit upper (lower)
 triangular matrices, and T is symmetric and band. The matrix T is
 then LU-factored with partial pivoting. The factored form of A
 is then used to solve the system of equations A * X = B.

 This is the blocked version of the algorithm, calling Level 3 BLAS.
Parameters
[in]UPLO
          UPLO is CHARACTER*1
          = 'U':  Upper triangle of A is stored;
          = 'L':  Lower triangle of A is stored.
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in]NRHS
          NRHS is INTEGER
          The number of right hand sides, i.e., the number of columns
          of the matrix B.  NRHS >= 0.
[in,out]A
          A is DOUBLE PRECISION array, dimension (LDA,N)
          On entry, the symmetric matrix A.  If UPLO = 'U', the leading
          N-by-N upper triangular part of A contains the upper
          triangular part of the matrix A, and the strictly lower
          triangular part of A is not referenced.  If UPLO = 'L', the
          leading N-by-N lower triangular part of A contains the lower
          triangular part of the matrix A, and the strictly upper
          triangular part of A is not referenced.

          On exit, L is stored below (or above) the subdiaonal blocks,
          when UPLO  is 'L' (or 'U').
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).
[out]TB
          TB is DOUBLE PRECISION array, dimension (LTB)
          On exit, details of the LU factorization of the band matrix.
[in]LTB
          LTB is INTEGER
          The size of the array TB. LTB >= 4*N, internally
          used to select NB such that LTB >= (3*NB+1)*N.

          If LTB = -1, then a workspace query is assumed; the
          routine only calculates the optimal size of LTB, 
          returns this value as the first entry of TB, and
          no error message related to LTB is issued by XERBLA.
[out]IPIV
          IPIV is INTEGER array, dimension (N)
          On exit, it contains the details of the interchanges, i.e.,
          the row and column k of A were interchanged with the
          row and column IPIV(k).
[out]IPIV2
          IPIV2 is INTEGER array, dimension (N)
          On exit, it contains the details of the interchanges, i.e.,
          the row and column k of T were interchanged with the
          row and column IPIV(k).
[in,out]B
          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
          On entry, the right hand side matrix B.
          On exit, the solution matrix X.
[in]LDB
          LDB is INTEGER
          The leading dimension of the array B.  LDB >= max(1,N).
[out]WORK
          WORK is DOUBLE PRECISION workspace of size LWORK
[in]LWORK
          LWORK is INTEGER
          The size of WORK. LWORK >= N, internally used to select NB
          such that LWORK >= N*NB.

          If LWORK = -1, then a workspace query is assumed; the
          routine only calculates the optimal size of the WORK array,
          returns this value as the first entry of the WORK array, and
          no error message related to LWORK is issued by XERBLA.
[out]INFO
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value.
          > 0:  if INFO = i, band LU factorization failed on i-th column
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 185 of file dsysv_aa_2stage.f.

188*
189* -- LAPACK computational routine --
190* -- LAPACK is a software package provided by Univ. of Tennessee, --
191* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
192*
193 IMPLICIT NONE
194*
195* .. Scalar Arguments ..
196 CHARACTER UPLO
197 INTEGER N, NRHS, LDA, LDB, LTB, LWORK, INFO
198* ..
199* .. Array Arguments ..
200 INTEGER IPIV( * ), IPIV2( * )
201 DOUBLE PRECISION A( LDA, * ), B( LDB, * ), TB( * ), WORK( * )
202* ..
203*
204* =====================================================================
205*
206* .. Local Scalars ..
207 LOGICAL UPPER, TQUERY, WQUERY
208 INTEGER LWKOPT
209* ..
210* .. External Functions ..
211 LOGICAL LSAME
212 EXTERNAL lsame
213* ..
214* .. External Subroutines ..
216 $ xerbla
217* ..
218* .. Intrinsic Functions ..
219 INTRINSIC max
220* ..
221* .. Executable Statements ..
222*
223* Test the input parameters.
224*
225 info = 0
226 upper = lsame( uplo, 'U' )
227 wquery = ( lwork.EQ.-1 )
228 tquery = ( ltb.EQ.-1 )
229 IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
230 info = -1
231 ELSE IF( n.LT.0 ) THEN
232 info = -2
233 ELSE IF( nrhs.LT.0 ) THEN
234 info = -3
235 ELSE IF( lda.LT.max( 1, n ) ) THEN
236 info = -5
237 ELSE IF( ltb.LT.( 4*n ) .AND. .NOT.tquery ) THEN
238 info = -7
239 ELSE IF( ldb.LT.max( 1, n ) ) THEN
240 info = -11
241 ELSE IF( lwork.LT.n .AND. .NOT.wquery ) THEN
242 info = -13
243 END IF
244*
245 IF( info.EQ.0 ) THEN
246 CALL dsytrf_aa_2stage( uplo, n, a, lda, tb, -1, ipiv,
247 $ ipiv2, work, -1, info )
248 lwkopt = int( work(1) )
249 END IF
250*
251 IF( info.NE.0 ) THEN
252 CALL xerbla( 'DSYSV_AA_2STAGE', -info )
253 RETURN
254 ELSE IF( wquery .OR. tquery ) THEN
255 RETURN
256 END IF
257*
258*
259* Compute the factorization A = U**T*T*U or A = L*T*L**T.
260*
261 CALL dsytrf_aa_2stage( uplo, n, a, lda, tb, ltb, ipiv, ipiv2,
262 $ work, lwork, info )
263 IF( info.EQ.0 ) THEN
264*
265* Solve the system A*X = B, overwriting B with X.
266*
267 CALL dsytrs_aa_2stage( uplo, n, nrhs, a, lda, tb, ltb, ipiv,
268 $ ipiv2, b, ldb, info )
269*
270 END IF
271*
272 work( 1 ) = lwkopt
273*
274 RETURN
275*
276* End of DSYSV_AA_2STAGE
277*
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine dsytrf_aa_2stage(UPLO, N, A, LDA, TB, LTB, IPIV, IPIV2, WORK, LWORK, INFO)
DSYTRF_AA_2STAGE
subroutine dsytrs_aa_2stage(UPLO, N, NRHS, A, LDA, TB, LTB, IPIV, IPIV2, B, LDB, INFO)
DSYTRS_AA_2STAGE
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