LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ csysv()

subroutine csysv ( character  uplo,
integer  n,
integer  nrhs,
complex, dimension( lda, * )  a,
integer  lda,
integer, dimension( * )  ipiv,
complex, dimension( ldb, * )  b,
integer  ldb,
complex, dimension( * )  work,
integer  lwork,
integer  info 
)

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

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

Purpose:
 CSYSV computes the solution to a complex 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.

 The diagonal pivoting method is used to factor A as
    A = U * D * U**T,  if UPLO = 'U', or
    A = L * D * L**T,  if UPLO = 'L',
 where U (or L) is a product of permutation and unit upper (lower)
 triangular matrices, and D is symmetric and block diagonal with
 1-by-1 and 2-by-2 diagonal blocks.  The factored form of A is then
 used to solve the system of equations A * X = B.
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 number of linear equations, i.e., 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 COMPLEX 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, if INFO = 0, the block diagonal matrix D and the
          multipliers used to obtain the factor U or L from the
          factorization A = U*D*U**T or A = L*D*L**T as computed by
          CSYTRF.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).
[out]IPIV
          IPIV is INTEGER array, dimension (N)
          Details of the interchanges and the block structure of D, as
          determined by CSYTRF.  If IPIV(k) > 0, then rows and columns
          k and IPIV(k) were interchanged, and D(k,k) is a 1-by-1
          diagonal block.  If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0,
          then rows and columns k-1 and -IPIV(k) were interchanged and
          D(k-1:k,k-1:k) is a 2-by-2 diagonal block.  If UPLO = 'L' and
          IPIV(k) = IPIV(k+1) < 0, then rows and columns k+1 and
          -IPIV(k) were interchanged and D(k:k+1,k:k+1) is a 2-by-2
          diagonal block.
[in,out]B
          B is COMPLEX array, dimension (LDB,NRHS)
          On entry, the N-by-NRHS right hand side matrix B.
          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
[in]LDB
          LDB is INTEGER
          The leading dimension of the array B.  LDB >= max(1,N).
[out]WORK
          WORK is COMPLEX array, dimension (MAX(1,LWORK))
          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
[in]LWORK
          LWORK is INTEGER
          The length of WORK.  LWORK >= 1, and for best performance
          LWORK >= max(1,N*NB), where NB is the optimal blocksize for
          CSYTRF.
          for LWORK < N, TRS will be done with Level BLAS 2
          for LWORK >= N, TRS will be done with Level BLAS 3

          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, D(i,i) is exactly zero.  The factorization
               has been completed, but the block diagonal matrix D is
               exactly singular, so the solution could not be computed.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 169 of file csysv.f.

171*
172* -- LAPACK driver routine --
173* -- LAPACK is a software package provided by Univ. of Tennessee, --
174* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
175*
176* .. Scalar Arguments ..
177 CHARACTER UPLO
178 INTEGER INFO, LDA, LDB, LWORK, N, NRHS
179* ..
180* .. Array Arguments ..
181 INTEGER IPIV( * )
182 COMPLEX A( LDA, * ), B( LDB, * ), WORK( * )
183* ..
184*
185* =====================================================================
186*
187* .. Local Scalars ..
188 LOGICAL LQUERY
189 INTEGER LWKOPT
190* ..
191* .. External Functions ..
192 LOGICAL LSAME
193 REAL SROUNDUP_LWORK
194 EXTERNAL lsame, sroundup_lwork
195* ..
196* .. External Subroutines ..
197 EXTERNAL xerbla, csytrf, csytrs, csytrs2
198* ..
199* .. Intrinsic Functions ..
200 INTRINSIC max
201* ..
202* .. Executable Statements ..
203*
204* Test the input parameters.
205*
206 info = 0
207 lquery = ( lwork.EQ.-1 )
208 IF( .NOT.lsame( uplo, 'U' ) .AND. .NOT.lsame( uplo, 'L' ) ) THEN
209 info = -1
210 ELSE IF( n.LT.0 ) THEN
211 info = -2
212 ELSE IF( nrhs.LT.0 ) THEN
213 info = -3
214 ELSE IF( lda.LT.max( 1, n ) ) THEN
215 info = -5
216 ELSE IF( ldb.LT.max( 1, n ) ) THEN
217 info = -8
218 ELSE IF( lwork.LT.1 .AND. .NOT.lquery ) THEN
219 info = -10
220 END IF
221*
222 IF( info.EQ.0 ) THEN
223 IF( n.EQ.0 ) THEN
224 lwkopt = 1
225 ELSE
226 CALL csytrf( uplo, n, a, lda, ipiv, work, -1, info )
227 lwkopt = int( work( 1 ) )
228 END IF
229 work( 1 ) = sroundup_lwork(lwkopt)
230 END IF
231*
232 IF( info.NE.0 ) THEN
233 CALL xerbla( 'CSYSV ', -info )
234 RETURN
235 ELSE IF( lquery ) THEN
236 RETURN
237 END IF
238*
239* Compute the factorization A = U*D*U**T or A = L*D*L**T.
240*
241 CALL csytrf( uplo, n, a, lda, ipiv, work, lwork, info )
242 IF( info.EQ.0 ) THEN
243*
244* Solve the system A*X = B, overwriting B with X.
245*
246 IF ( lwork.LT.n ) THEN
247*
248* Solve with TRS ( Use Level BLAS 2)
249*
250 CALL csytrs( uplo, n, nrhs, a, lda, ipiv, b, ldb, info )
251*
252 ELSE
253*
254* Solve with TRS2 ( Use Level BLAS 3)
255*
256 CALL csytrs2( uplo,n,nrhs,a,lda,ipiv,b,ldb,work,info )
257*
258 END IF
259*
260 END IF
261*
262 work( 1 ) = sroundup_lwork(lwkopt)
263*
264 RETURN
265*
266* End of CSYSV
267*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
subroutine csytrf(uplo, n, a, lda, ipiv, work, lwork, info)
CSYTRF
Definition csytrf.f:182
subroutine csytrs2(uplo, n, nrhs, a, lda, ipiv, b, ldb, work, info)
CSYTRS2
Definition csytrs2.f:132
subroutine csytrs(uplo, n, nrhs, a, lda, ipiv, b, ldb, info)
CSYTRS
Definition csytrs.f:120
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
real function sroundup_lwork(lwork)
SROUNDUP_LWORK
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