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 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).

               = 0: successful exit
               < 0: if INFO = -k, the k-th argument had an  ille­
               gal value


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