NAME

dsttrs - computes the solution to a real system of linear equations A * X = B

SYNOPSIS

  SUBROUTINE DSTTRS( N, NRHS, L, D, SUBL, B, LDB, IPIV, INFO)
  INTEGER N, NRHS, LDB, INFO
  INTEGER IPIV(*)
  DOUBLE PRECISION L(*), D(*), SUBL(*), B(LDB,*)

  SUBROUTINE DSTTRS_64( N, NRHS, L, D, SUBL, B, LDB, IPIV, INFO)
  INTEGER*8 N, NRHS, LDB, INFO
  INTEGER*8 IPIV(*)
  DOUBLE PRECISION L(*), D(*), SUBL(*), B(LDB,*)

F95 INTERFACE

  SUBROUTINE STTRS( [N], [NRHS], L, D, SUBL, B, [LDB], IPIV, [INFO])
  INTEGER :: N, NRHS, LDB, INFO
  INTEGER, DIMENSION(:) :: IPIV
  REAL(8), DIMENSION(:) :: L, D, SUBL
  REAL(8), DIMENSION(:,:) :: B

  SUBROUTINE STTRS_64( [N], [NRHS], L, D, SUBL, B, [LDB], IPIV, [INFO])
  INTEGER(8) :: N, NRHS, LDB, INFO
  INTEGER(8), DIMENSION(:) :: IPIV
  REAL(8), DIMENSION(:) :: L, D, SUBL
  REAL(8), DIMENSION(:,:) :: B

C INTERFACE

#include <sunperf.h>

void dsttrs(int n, int nrhs, double *l, double *d, double *subl, double *b, int ldb, int *ipiv, int *info);

void dsttrs_64(long n, long nrhs, double *l, double *d, double *subl, double *b, long ldb, long *ipiv, long *info);

PURPOSE

dsttrs computes the solution to a real system of linear equations A * X = B, where A is an N-by-N symmetric tridiagonal matrix and X and B are N-by-NRHS matrices.

ARGUMENTS

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.
L (input)
```
 REAL array, dimension (N-1)
```
On entry, the subdiagonal elements of LL and DD.
D (input)
```
 REAL array, dimension (N)
```
On entry, the diagonal elements of DD.
SUBL (input)
```
 REAL array, dimension (N-2)
```
On entry, the second subdiagonal elements of LL.
B (input)
```
 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 (input)
```
 INTEGER
```
The leading dimension of the array B. LDB > = max(1, N)
IPIV (output)
```
 INTEGER array, dimension (N)
```
Details of the interchanges and block pivot. If IPIV(K) > 0, 1 by 1 pivot, and if IPIV(K) = K + 1 an interchange done; If IPIV(K) < 0, 2 by 2 pivot, no interchange required.

INFO (output)

 INTEGER

 = 0:  successful exit

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