SRC/ssysv_aa.f(3)          Library Functions Manual          SRC/ssysv_aa.f(3)

NAME
       SRC/ssysv_aa.f

SYNOPSIS
   Functions/Subroutines
       subroutine ssysv_aa (uplo, n, nrhs, a, lda, ipiv, b, ldb, work, lwork,
           info)
            SSYSV_AA computes the solution to system of linear equations A * X
           = B for SY matrices

Function/Subroutine Documentation
   subroutine ssysv_aa (character uplo, integer n, integer nrhs, real,
       dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, real,
       dimension( ldb, * ) b, integer ldb, real, dimension( * ) work, integer
       lwork, integer info)
        SSYSV_AA computes the solution to system of linear equations A * X = B
       for SY matrices

       Purpose:


            SSYSV 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 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 tridiagonal. The factored
            form of A is then used to solve the system of equations A * X = B.

       Parameters
           UPLO

                     UPLO is CHARACTER*1
                     = 'U':  Upper triangle of A is stored;
                     = 'L':  Lower triangle of A is stored.

           N

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

           NRHS

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

           A

                     A is REAL 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 tridiagonal matrix T and the
                     multipliers used to obtain the factor U or L from the
                     factorization A = U**T*T*U or A = L*T*L**T as computed by
                     SSYTRF.

           LDA

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

           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).

           B

                     B is REAL 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.

           LDB

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

           WORK

                     WORK is REAL array, dimension (MAX(1,LWORK))
                     On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

           LWORK

                     LWORK is INTEGER
                     The length of WORK.  LWORK >= MAX(1,2*N,3*N-2), and for
                     the best performance, LWORK >= MAX(1,N*NB), where NB is
                     the optimal blocksize for SSYTRF_AA.

                     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.

           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 160 of file ssysv_aa.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

LAPACK                          Version 3.12.0               SRC/ssysv_aa.f(3)