STRTRI - compute the inverse of a real upper or lower tri
angular matrix A
SYNOPSIS
SUBROUTINE STRTRI( UPLO, DIAG, N, A, LDA, INFO )
CHARACTER DIAG, UPLO
INTEGER INFO, LDA, N
REAL A( LDA, * )
PURPOSE
STRTRI computes the inverse of a real upper or lower tri
angular 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 non-unit triangular;
= 'U': A is unit triangular.
N (input) INTEGER
The order of the matrix A. N >= 0.
A (input/output) REAL 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 triangular matrix, and the strictly upper
triangular part of A is not referenced. If DIAG =
'U', the diagonal elements of A are also not ref
erenced 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 i-th argument had an ille
gal value
> 0: if INFO = i, A(i,i) is exactly zero. The
not be computed.
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