dppcon man page on Scientific

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DPPCON(1)		 LAPACK routine (version 3.2)		     DPPCON(1)

NAME
       DPPCON  -  estimates  the  reciprocal  of  the condition number (in the
       1-norm) of a real symmetric positive definite packed matrix  using  the
       Cholesky factorization A = U**T*U or A = L*L**T computed by DPPTRF

SYNOPSIS
       SUBROUTINE DPPCON( UPLO, N, AP, ANORM, RCOND, WORK, IWORK, INFO )

	   CHARACTER	  UPLO

	   INTEGER	  INFO, N

	   DOUBLE	  PRECISION ANORM, RCOND

	   INTEGER	  IWORK( * )

	   DOUBLE	  PRECISION AP( * ), WORK( * )

PURPOSE
       DPPCON estimates the reciprocal of the condition number (in the 1-norm)
       of a real symmetric positive definite packed matrix using the  Cholesky
       factorization A = U**T*U or A = L*L**T computed by DPPTRF.  An estimate
       is obtained for norm(inv(A)), and the reciprocal of the condition  num‐
       ber is computed as RCOND = 1 / (ANORM * norm(inv(A))).

ARGUMENTS
       UPLO    (input) CHARACTER*1
	       = 'U':  Upper triangle of A is stored;
	       = 'L':  Lower triangle of A is stored.

       N       (input) INTEGER
	       The order of the matrix A.  N >= 0.

       AP      (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
	       The  triangular factor U or L from the Cholesky factorization A
	       = U**T*U or A = L*L**T, packed columnwise in  a	linear	array.
	       The j-th column of U or L is stored in the array AP as follows:
	       if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j; if  UPLO
	       = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.

       ANORM   (input) DOUBLE PRECISION
	       The 1-norm (or infinity-norm) of the symmetric matrix A.

       RCOND   (output) DOUBLE PRECISION
	       The  reciprocal	of  the condition number of the matrix A, com‐
	       puted as RCOND = 1/(ANORM * AINVNM), where AINVNM is  an	 esti‐
	       mate of the 1-norm of inv(A) computed in this routine.

       WORK    (workspace) DOUBLE PRECISION array, dimension (3*N)

       IWORK   (workspace) INTEGER array, dimension (N)

       INFO    (output) INTEGER
	       = 0:  successful exit
	       < 0:  if INFO = -i, the i-th argument had an illegal value

 LAPACK routine (version 3.2)	 November 2008			     DPPCON(1)
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