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NAME
     dtrtri - compute the inverse of a real upper or  lower  tri-
     angular matrix A

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

     CHARACTER DIAG, UPLO

     INTEGER INFO, LDA, N

     DOUBLE PRECISION A( LDA, * )



     #include <sunperf.h>

     void dtrtri(char uplo, char diag, int  n,  double  *da,  int
               lda, int *info) ;

PURPOSE
     DTRTRI computes the inverse of a real upper  or  lower  tri-
     angular 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 non-unit 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  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  ille-
               gal value
               > 0: if INFO = i, A(i,i)  is  exactly  zero.   The
               triangular  matrix is singular and its inverse can
               not be computed.

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