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

SYNOPSIS
     SUBROUTINE DSTTRS(N, NRHS, L, D, SUBL, B, LDB, IPIV, INFO )

     INTEGER           N, NRHS, LDB, IPIV( * ), INFO

     DOUBLE PRECISION  D( * ), L( * ), SUBL( * ), B( * )



     #include <sunperf.h>

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

PURPOSE
     DSTTRS computes the solution to a double precision 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) DOUBLE PRECISION array, dimension (N-1)
               On entry, the subdiagonal elements of LL and DD.

     D         (input) DOUBLE PRECISION array, dimension (N)
               On entry, the diagonal elements of DD.

     SUBL      (input) DOUBLE PRECISION array, dimension (N-2)
               On entry, the second subdiagonal elements of LL.

     B         (input/output) DOUBLE PRECISION 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 ille-
               gal value

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