
DTRTRI(l) ) DTRTRI(l)
NAME
DTRTRI  compute the inverse of a real upper or lower triangular 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 triangular matrix A. This is the
Level 3 BLAS version of the algorithm.
ARGUMENTS
UPLO (input) CHARACTER*1
= 'U': A is upper triangular;
= 'L': A is lower triangular.
DIAG (input) CHARACTER*1
= 'N': A is nonunit 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 NbyN upper trian
gular 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 NbyN
lower triangular part of the array A contains the lower triangular matrix, and the
strictly upper triangular part of A is not referenced. If DIAG = 'U', the diago
nal elements of A are also not referenced and are assumed to be 1. On exit, the
(triangular) 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 ith argument had an illegal value
> 0: if INFO = i, A(i,i) is exactly zero. The triangular matrix is singular and
its inverse can not be computed.
LAPACK version 3.0 15 June 2000 DTRTRI(l) 
