DTRTRI(3)
computes 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 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 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
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 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.