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

NAME

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

SYNOPSIS

  SUBROUTINE DPTSV( N, NRHS, DIAG, SUB, B, LDB, INFO)
  INTEGER N, NRHS, LDB, INFO
  DOUBLE PRECISION DIAG(*), SUB(*), B(LDB,*)

  SUBROUTINE DPTSV_64( N, NRHS, DIAG, SUB, B, LDB, INFO)
  INTEGER*8 N, NRHS, LDB, INFO
  DOUBLE PRECISION DIAG(*), SUB(*), B(LDB,*)

F95 INTERFACE

  SUBROUTINE PTSV( [N], [NRHS], DIAG, SUB, B, [LDB], [INFO])
  INTEGER :: N, NRHS, LDB, INFO
  REAL(8), DIMENSION(:) :: DIAG, SUB
  REAL(8), DIMENSION(:,:) :: B

  SUBROUTINE PTSV_64( [N], [NRHS], DIAG, SUB, B, [LDB], [INFO])
  INTEGER(8) :: N, NRHS, LDB, INFO
  REAL(8), DIMENSION(:) :: DIAG, SUB
  REAL(8), DIMENSION(:,:) :: B

C INTERFACE

#include <sunperf.h>

void dptsv(int n, int nrhs, double *diag, double *sub, double *b, int ldb, int *info);

void dptsv_64(long n, long nrhs, double *diag, double *sub, double *b, long ldb, long *info);

PURPOSE

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

A is factored as A = L*D*L**T, and the factored form of A is then used to solve the system of equations.

ARGUMENTS

• N (input)
  The order of the 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/output)
  On entry, the n diagonal elements of the tridiagonal matrix A. On exit, the n diagonal elements of the diagonal matrix DIAG from the factorization A = L*DIAG*L**T.

• SUB (input/output)
  On entry, the (n-1) subdiagonal elements of the tridiagonal matrix A. On exit, the (n-1) subdiagonal elements of the unit bidiagonal factor L from the L*DIAG*L**T factorization of A. (SUB can also be regarded as the superdiagonal of the unit bidiagonal factor U from the U**T*DIAG*U factorization of A.)

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

• INFO (output)
  

   = 0:  successful exit

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

   > 0:  if INFO  = i, the leading minor of order i is not
  positive definite, and the solution has not been
  computed.  The factorization has not been completed
  unless i  = N.