spttrf

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)