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

NAME

spttrf - compute the L*D*L' factorization of a real symmetric positive definite tridiagonal matrix A

SYNOPSIS

  SUBROUTINE SPTTRF( N, DIAG, OFFD, INFO)
  INTEGER N, INFO
  REAL DIAG(*), OFFD(*)

  SUBROUTINE SPTTRF_64( N, DIAG, OFFD, INFO)
  INTEGER*8 N, INFO
  REAL DIAG(*), OFFD(*)

F95 INTERFACE

  SUBROUTINE PTTRF( [N], DIAG, OFFD, [INFO])
  INTEGER :: N, INFO
  REAL, DIMENSION(:) :: DIAG, OFFD

  SUBROUTINE PTTRF_64( [N], DIAG, OFFD, [INFO])
  INTEGER(8) :: N, INFO
  REAL, DIMENSION(:) :: DIAG, OFFD

C INTERFACE

#include <sunperf.h>

void spttrf(int n, float *diag, float *offd, int *info);

void spttrf_64(long n, float *diag, float *offd, long *info);

PURPOSE

spttrf computes the L*D*L' factorization of a real symmetric positive definite tridiagonal matrix A. The factorization may also be regarded as having the form A = U'*D*U.

ARGUMENTS

• N (input)
  The order of the matrix A. N > = 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 L*DIAG*L' factorization of A.

• OFFD (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' factorization of A. OFFD can also be regarded as the superdiagonal of the unit bidiagonal factor U from the U'*DIAG*U factorization of A.

• INFO (output)
  

   = 0: successful exit

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

   > 0: if INFO  = k, the leading minor of order k is not
  positive definite; if k  < N, the factorization could not
  be completed, while if k  = N, the factorization was
  completed, but DIAG(N)  = 0.