NAME

spttrf - compute the factorization of a real symmetric positive definite tridiagonal matrix A

SYNOPSIS

SUBROUTINE SPTTRF( N, D, E, INFO )

INTEGER INFO, N

REAL D( ∗ ), E( ∗ )

#include <sunperf.h>

void spttrf(int n, float ∗d, float ∗e, int ∗info) ;

PURPOSE

SPTTRF computes the factorization of a real symmetric positive definite tridiagonal matrix A. 
 
If the subdiagonal elements of A are supplied in the array E, the factorization has the form A = L∗D∗L∗∗T, where D is diagonal and L is unit lower bidiagonal; if the superdiagonal elements of A are supplied, it has the form A = U∗∗T∗D∗U, where U is unit upper bidiagonal.  (The two forms are equivalent if A is real.)
 

ARGUMENTS

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

D (input/output) REAL array, dimension (N)
On entry, the n diagonal elements of the tridiagonal matrix A.  On exit, the n diagonal elements of the diagonal matrix D from the L∗D∗L∗∗T factorization of A.

E (input/output) REAL array, dimension (N-1)
On entry, the (n-1) off-diagonal elements of the tridiagonal matrix A. On exit, the (n-1) off-diagonal elements of the unit bidiagonal factor L or U from the factorization of A.

INFO (output) INTEGER
= 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; if i < N, the factorization could not be completed, while if i = N, the factorization was completed, but D(N) = 0.

SunOS 5.0  —  Last change: 10 Dec 1998