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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