man strtri (Fonctions bibliothèques) - compute the inverse of a real upper or lower triangular matrix A

NAME

STRTRI - compute the inverse of a real upper or lower triangular matrix A

STRTRI computes the inverse of a real upper or lower triangular matrix A. This is the Level 3 BLAS version of the algorithm.

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 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 i-th 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.