dtrtri(3)

NAME

DTRTRI - compute the inverse of a real upper or lower tri

angular matrix A

SYNOPSIS

SUBROUTINE DTRTRI( UPLO, DIAG, N, A, LDA, INFO )
    CHARACTER      DIAG, UPLO
    INTEGER        INFO, LDA, N
    DOUBLE         PRECISION A( LDA, * )

PURPOSE

DTRTRI computes the inverse of a real upper or lower tri

angular matrix A. This is the Level 3 BLAS version of the algo

rithm.

ARGUMENTS

UPLO (input) CHARACTER*1

= 'U': A is upper triangular;
= 'L': A is lower triangular.

DIAG (input) CHARACTER*1

= 'N': A is non-unit triangular;
= 'U': A is unit triangular.

N (input) INTEGER

The order of the matrix A. N >= 0.

A (input/output) DOUBLE PRECISION array, dimension

(LDA,N)

On entry, the triangular matrix A. If UPLO = 'U',

the leading N-by-N upper triangular part of the array A contains

the upper triangular matrix, and the strictly lower triangular

part of A is not referenced. If UPLO = 'L', the leading N-by-N

lower triangular part of the array A contains the lower triangu

lar matrix, and the strictly upper triangular part of A is not

referenced. If DIAG = 'U', the diagonal elements of A are also

not referenced and are assumed to be 1. On exit, the (triangu

lar) inverse of the original matrix, in the same storage format.

LDA (input) INTEGER

The leading dimension of the array A. LDA >=

max(1,N).

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille

gal value
> 0: if INFO = i, A(i,i) is exactly zero. The

triangular matrix is singular and its inverse can not be comput

ed.

LAPACK version 3.0 15 June 2000

DTRTRI(3)