SYNOPSIS

SUBROUTINE DSYTRS(

UPLO, N, NRHS, A, LDA, IPIV, B, LDB, INFO )

    

CHARACTER UPLO

    

INTEGER INFO, LDA, LDB, N, NRHS

    

INTEGER IPIV( * )

    

DOUBLE PRECISION A( LDA, * ), B( LDB, * )

PURPOSE

DSYTRS solves a system of linear equations A*X = B with a real symmetric matrix A using the factorization A = U*D*U**T or A = L*D*L**T computed by DSYTRF.

ARGUMENTS

UPLO (input) CHARACTER*1

Specifies whether the details of the factorization are stored as an upper or lower triangular matrix. = 'U': Upper triangular, form is A = U*D*U**T;
= 'L': Lower triangular, form is A = L*D*L**T.

N (input) INTEGER

The order of the matrix A. N >= 0.

NRHS (input) INTEGER

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

A (input) DOUBLE PRECISION array, dimension (LDA,N)

The block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by DSYTRF.

LDA (input) INTEGER

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

IPIV (input) INTEGER array, dimension (N)

Details of the interchanges and the block structure of D as determined by DSYTRF.

B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)

On entry, the right hand side matrix B. On exit, the solution matrix X.

LDB (input) INTEGER

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

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value