redhat man page for dtrtri

DTRTRI(l)								 )								 DTRTRI(l)

NAME
       DTRTRI - compute the inverse of a real upper or lower triangular matrix A

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

	   CHARACTER	  DIAG, UPLO

	   INTEGER	  INFO, LDA, N

	   DOUBLE	  PRECISION A( LDA, * )

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

LAPACK version 3.0						   15 June 2000 							 DTRTRI(l)