NAME

dsttrf - compute the factorization of a symmetric tridiagonal matrix A

SYNOPSIS

  SUBROUTINE DSTTRF( N, L, D, SUBL, IPIV, INFO)
  INTEGER N, INFO
  INTEGER IPIV(*)
  DOUBLE PRECISION L(*), D(*), SUBL(*)

  SUBROUTINE DSTTRF_64( N, L, D, SUBL, IPIV, INFO)
  INTEGER*8 N, INFO
  INTEGER*8 IPIV(*)
  DOUBLE PRECISION L(*), D(*), SUBL(*)

F95 INTERFACE

  SUBROUTINE STTRF( [N], L, D, SUBL, IPIV, [INFO])
  INTEGER :: N, INFO
  INTEGER, DIMENSION(:) :: IPIV
  REAL(8), DIMENSION(:) :: L, D, SUBL

  SUBROUTINE STTRF_64( [N], L, D, SUBL, IPIV, [INFO])
  INTEGER(8) :: N, INFO
  INTEGER(8), DIMENSION(:) :: IPIV
  REAL(8), DIMENSION(:) :: L, D, SUBL

C INTERFACE

#include <sunperf.h>

void dsttrf(int n, double *l, double *d, double *subl, int *ipiv, int *info);

void dsttrf_64(long n, double *l, double *d, double *subl, long *ipiv, long *info);

PURPOSE

dsttrf computes the factorization of a complex Hermitian tridiagonal matrix A.

ARGUMENTS

N (input)
```
 INTEGER
```
The order of the matrix A. N > = 0.
L (input/output)
```
 REAL array, dimension (N)
```
On entry, the n-1 subdiagonal elements of the tridiagonal matrix A. On exit, part of the factorization of A.
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**H factorization of A.
SUBL (output)
```
 REAL array, dimension (N)
```
On exit, part of the factorization of A.
IPIV (output)
```
 INTEGER array, dimension (N)
```
On exit, the pivot indices of the factorization.

INFO (output)

 INTEGER

 = 0:  successful exit

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

 > 0:  if INFO  = i, D(k,k) is exactly zero.  The factorization has
been completed, but the block diagonal matrix D is exactly singular
and division by zero will occur if it is used to solve a system of
equations.