Contents

• NAME
• SYNOPSIS
  • F95 INTERFACE
  • C INTERFACE
• PURPOSE
• ARGUMENTS

NAME

     dpttrs - solve a tridiagonal system of the form  A * X  =  B
     using the L*D*L' factorization of A computed by DPTTRF

SYNOPSIS

     SUBROUTINE DPTTRS(N, NRHS, D, E, B, LDB, INFO)

     INTEGER N, NRHS, LDB, INFO
     DOUBLE PRECISION D(*), E(*), B(LDB,*)

     SUBROUTINE DPTTRS_64(N, NRHS, D, E, B, LDB, INFO)

     INTEGER*8 N, NRHS, LDB, INFO
     DOUBLE PRECISION D(*), E(*), B(LDB,*)

  F95 INTERFACE
     SUBROUTINE PTTRS([N], [NRHS], D, E, B, [LDB], [INFO])

     INTEGER :: N, NRHS, LDB, INFO
     REAL(8), DIMENSION(:) :: D, E
     REAL(8), DIMENSION(:,:) :: B

     SUBROUTINE PTTRS_64([N], [NRHS], D, E, B, [LDB], [INFO])

     INTEGER(8) :: N, NRHS, LDB, INFO
     REAL(8), DIMENSION(:) :: D, E
     REAL(8), DIMENSION(:,:) :: B

  C INTERFACE
     #include <sunperf.h>

     void dpttrs(int n, int nrhs, double *d,  double  *e,  double
               *b, int ldb, int *info);

     void dpttrs_64(long n, long nrhs, double *d, double *e, dou-
               ble *b, long ldb, long *info);

PURPOSE

     dpttrs solves a tridiagonal system of the form
        A * X = B using the L*D*L' factorization of A computed by
     DPTTRF.  D is a diagonal matrix specified in the vector D, L
     is a unit bidiagonal matrix whose subdiagonal  is  specified
     in the vector E, and X and B are N by NRHS matrices.

ARGUMENTS

     N (input) The order of the tridiagonal matrix A.  N >= 0.

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

     D (input) The n diagonal elements of the diagonal  matrix  D
               from the L*D*L' factorization of A.

     E (input) The (n-1) subdiagonal elements of the unit bidiag-
               onal  factor L from the L*D*L' factorization of A.
               E can also be regarded as the superdiagonal of the
               unit  bidiagonal factor U from the factorization A
               = U'*D*U.

     B (input/output)
               On entry, the right hand side vectors  B  for  the
               system of linear equations.  On exit, the solution
               vectors, X.

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

     INFO (output)
               = 0: successful exit
               < 0: if INFO = -k, the k-th argument had an  ille-
               gal value