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# dsptrs

```
NAME
DSPTRS - solve a system of linear equations A*X = B with a
real symmetric matrix A stored in packed format using the
factorization A = U*D*U**T or A = L*D*L**T computed by
DSPTRF

SYNOPSIS
SUBROUTINE DSPTRS( UPLO, N, NRHS, AP, IPIV, B, LDB, INFO )

CHARACTER      UPLO

INTEGER        INFO, LDB, N, NRHS

INTEGER        IPIV( * )

DOUBLE         PRECISION AP( * ), B( LDB, * )

PURPOSE
DSPTRS solves a system of linear equations A*X = B with a
real symmetric matrix A stored in packed format using the
factorization A = U*D*U**T or A = L*D*L**T computed by
DSPTRF.

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.

AP      (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
The block diagonal matrix D and the multipliers used
to obtain the factor U or L as computed by DSPTRF,
stored as a packed triangular matrix.

IPIV    (input) INTEGER array, dimension (N)
Details of the interchanges and the block structure
of D as determined by DSPTRF.

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