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


SYNOPSIS

       SUBROUTINE STRTRI( UPLO, DIAG, N, A, LDA, INFO )

           CHARACTER      DIAG, UPLO

           INTEGER        INFO, LDA, N

           REAL           A( LDA, * )


PURPOSE

       STRTRI 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) REAL 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).

       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

               not be computed.


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