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RedHat 9 (Linux i386) - man page for dtptri (redhat section l)

DTPTRI(l)					)					DTPTRI(l)

NAME
       DTPTRI - compute the inverse of a real upper or lower triangular matrix A stored in packed
       format

SYNOPSIS
       SUBROUTINE DTPTRI( UPLO, DIAG, N, AP, INFO )

	   CHARACTER	  DIAG, UPLO

	   INTEGER	  INFO, N

	   DOUBLE	  PRECISION AP( * )

PURPOSE
       DTPTRI computes the inverse of a real upper or lower triangular matrix A stored in  packed
       format.

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.

       AP      (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
	       On  entry,  the	upper or lower triangular matrix A, stored columnwise in a linear
	       array.  The j-th column of A is stored in the array AP as follows: if UPLO =  'U',
	       AP(i  + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*((2*n-j)/2) =
	       A(i,j) for j<=i<=n.  See below for further details.   On  exit,	the  (triangular)
	       inverse of the original matrix, in the same packed storage format.

       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.

FURTHER DETAILS
       A triangular matrix A can be transferred to packed storage using one of the following pro-
       gram segments:

       UPLO = 'U':			UPLO = 'L':

	     JC = 1			      JC = 1
	     DO 2 J = 1, N		      DO 2 J = 1, N
		DO 1 I = 1, J			 DO 1 I = J, N
		   AP(JC+I-1) = A(I,J)		    AP(JC+I-J) = A(I,J)
	   1	CONTINUE		    1	 CONTINUE
		JC = JC + J			 JC = JC + N - J + 1
	   2 CONTINUE			    2 CONTINUE

LAPACK version 3.0			   15 June 2000 				DTPTRI(l)


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