NAME

SYNOPSIS

  SUBROUTINE ZSYSV( UPLO, N, NRHS, A, LDA, IPIVOT, B, LDB, WORK, 
 *      LDWORK, INFO)
  CHARACTER * 1 UPLO
  DOUBLE COMPLEX A(LDA,*), B(LDB,*), WORK(*)
  INTEGER N, NRHS, LDA, LDB, LDWORK, INFO
  INTEGER IPIVOT(*)
 
  SUBROUTINE ZSYSV_64( UPLO, N, NRHS, A, LDA, IPIVOT, B, LDB, WORK, 
 *      LDWORK, INFO)
  CHARACTER * 1 UPLO
  DOUBLE COMPLEX A(LDA,*), B(LDB,*), WORK(*)
  INTEGER*8 N, NRHS, LDA, LDB, LDWORK, INFO
  INTEGER*8 IPIVOT(*)
 

F95 INTERFACE

  SUBROUTINE SYSV( UPLO, N, NRHS, A, [LDA], IPIVOT, B, [LDB], [WORK], 
 *       [LDWORK], [INFO])
  CHARACTER(LEN=1) :: UPLO
  COMPLEX(8), DIMENSION(:) :: WORK
  COMPLEX(8), DIMENSION(:,:) :: A, B
  INTEGER :: N, NRHS, LDA, LDB, LDWORK, INFO
  INTEGER, DIMENSION(:) :: IPIVOT
 
  SUBROUTINE SYSV_64( UPLO, N, NRHS, A, [LDA], IPIVOT, B, [LDB], [WORK], 
 *       [LDWORK], [INFO])
  CHARACTER(LEN=1) :: UPLO
  COMPLEX(8), DIMENSION(:) :: WORK
  COMPLEX(8), DIMENSION(:,:) :: A, B
  INTEGER(8) :: N, NRHS, LDA, LDB, LDWORK, INFO
  INTEGER(8), DIMENSION(:) :: IPIVOT
 

C INTERFACE

void zsysv(char uplo, int n, int nrhs, doublecomplex *a, int lda, int *ipivot, doublecomplex *b, int ldb, int *info);

void zsysv_64(char uplo, long n, long nrhs, doublecomplex *a, long lda, long *ipivot, doublecomplex *b, long ldb, long *info);

PURPOSE

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.

ARGUMENTS

* UPLO (input)

* N (input)

The number of linear equations, i.e., the order of the matrix A. N >= 0.

* NRHS (input)

The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0.

* A (input/output)

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.

* LDA (input)

The leading dimension of the array A. LDA >= max(1,N).

* IPIVOT (output)

Details of the interchanges and the block structure of D, as determined by CSYTRF. If IPIVOT(k) > 0, then rows and columns k and IPIVOT(k) were interchanged, and D(k,k) is a 1-by-1 diagonal block. If UPLO = 'U' and IPIVOT(k) = IPIVOT(k-1) < 0, then rows and columns k-1 and -IPIVOT(k) were interchanged and D(k-1:k,k-1:k) is a 2-by-2 diagonal block. If UPLO = 'L' and IPIVOT(k) = IPIVOT(k+1) < 0, then rows and columns k+1 and -IPIVOT(k) were interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.

* B (input/output)

On entry, the N-by-NRHS right hand side matrix B. On exit, if INFO = 0, the N-by-NRHS solution matrix X.

* LDB (input)

The leading dimension of the array B. LDB >= max(1,N).

* WORK (workspace)

On exit, if INFO = 0, WORK(1) returns the optimal LDWORK.

* LDWORK (input)

The length of WORK. LDWORK >= 1, and for best performance LDWORK >= N*NB, where NB is the optimal blocksize for CSYTRF.

If LDWORK = -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 LDWORK is issued by XERBLA.

* INFO (output)