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dtrti2

```
NAME
DTRTI2 - compute the inverse of a real upper or lower tri-
angular matrix

SYNOPSIS
SUBROUTINE DTRTI2( UPLO, DIAG, N, A, LDA, INFO )

CHARACTER      DIAG, UPLO

INTEGER        INFO, LDA, N

DOUBLE         PRECISION A( LDA, * )

PURPOSE
DTRTI2 computes the inverse of a real upper or lower tri-
angular matrix.

This is the Level 2 BLAS version of the algorithm.

ARGUMENTS
UPLO    (input) CHARACTER*1
Specifies whether the matrix A is upper or lower
triangular.  = 'U':  Upper triangular
= 'L':  Lower triangular

DIAG    (input) CHARACTER*1
Specifies whether or not the matrix A is unit tri-
angular.  = 'N':  Non-unit triangular
= 'U':  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
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 = -k, the k-th argument had an illegal
value
```