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 SPTTRF

SYNOPSIS

     SUBROUTINE DPTTRS(N, NRHS, DIAG, OFFD, B, LDB, INFO)

     INTEGER N, NRHS, LDB, INFO
     DOUBLE PRECISION DIAG(*), OFFD(*), B(LDB,*)

     SUBROUTINE DPTTRS_64(N, NRHS, DIAG, OFFD, B, LDB, INFO)

     INTEGER*8 N, NRHS, LDB, INFO
     DOUBLE PRECISION DIAG(*), OFFD(*), B(LDB,*)

  F95 INTERFACE
     SUBROUTINE PTTRS([N], [NRHS], DIAG, OFFD, B, [LDB], [INFO])

     INTEGER :: N, NRHS, LDB, INFO
     REAL(8), DIMENSION(:) :: DIAG, OFFD
     REAL(8), DIMENSION(:,:) :: B

     SUBROUTINE PTTRS_64([N], [NRHS], DIAG, OFFD, B, [LDB], [INFO])

     INTEGER(8) :: N, NRHS, LDB, INFO
     REAL(8), DIMENSION(:) :: DIAG, OFFD
     REAL(8), DIMENSION(:,:) :: B

  C INTERFACE
     #include <sunperf.h>

     void dpttrs(int n, int nrhs,  double  *diag,  double  *offd,
               double *b, int ldb, int *info);

     void dpttrs_64(long  n,  long  nrhs,  double  *diag,  double
               *offd, double *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
     SPTTRF.  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.

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

     OFFD (input/output)
               The (n-1) subdiagonal elements of the unit bidiag-
               onal  factor L from the L*DIAG*L' factorization of
               A.  OFFD can also be regarded as the superdiagonal
               of  the unit bidiagonal factor U from the factori-
               zation A = U'*DIAG*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