DSYTRS2 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 and converted by DSYCONV.

UPLO

          UPLO is 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

          N is INTEGER


          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 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.


          Note that A is input / output. This might be counter-intuitive,


          and one may think that A is input only. A is input / output. This


          is because, at the start of the subroutine, we permute A in a


          "better" form and then we permute A back to its original form at


          the end.

LDA

          LDA is INTEGER


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

IPIV

          IPIV is INTEGER array, dimension (N)


          Details of the interchanges and the block structure of D


          as determined by DSYTRF.

B

          B is DOUBLE PRECISION array, dimension (LDB,NRHS)


          On entry, the right hand side matrix B.


          On exit, the solution matrix X.

LDB

          LDB is INTEGER


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

WORK

          WORK is DOUBLE PRECISION array, dimension (N)

INFO

          INFO is INTEGER


          = 0:  successful exit


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

Univ. of Tennessee

Univ. of California Berkeley

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NAG Ltd.

June 2016