dgsequ.c File Reference

Computes row and column scalings. More...

#include <math.h>
#include "slu_ddefs.h"

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Functions
void	dgsequ (SuperMatrix *A, double *r, double *c, double *rowcnd, double *colcnd, double *amax, int *info)
	Driver related. More...

Detailed Description

Copyright (c) 2003, The Regents of the University of California, through Lawrence Berkeley National Laboratory (subject to receipt of any required approvals from U.S. Dept. of Energy)

All rights reserved.

The source code is distributed under BSD license, see the file License.txt at the top-level directory.

– SuperLU routine (version 2.0) –
Univ. of California Berkeley, Xerox Palo Alto Research Center,
and Lawrence Berkeley National Lab.
November 15, 1997

Modified from LAPACK routine DGEEQU

Function Documentation

void dgsequ	(	SuperMatrix *	A,
		double *	r,
		double *	c,
		double *	rowcnd,
		double *	colcnd,
		double *	amax,
		int *	info
	)

Purpose   

  DGSEQU computes row and column scalings intended to equilibrate an   
  M-by-N sparse matrix A and reduce its condition number. R returns the row
  scale factors and C the column scale factors, chosen to try to make   
  the largest element in each row and column of the matrix B with   
  elements B(i,j)=R(i)*A(i,j)*C(j) have absolute value 1.

  R(i) and C(j) are restricted to be between SMLNUM = smallest safe   
  number and BIGNUM = largest safe number.  Use of these scaling   
  factors is not guaranteed to reduce the condition number of A but   
  works well in practice.

  See supermatrix.h for the definition of 'SuperMatrix' structure.

Arguments   

  A       (input) SuperMatrix*
          The matrix of dimension (A->nrow, A->ncol) whose equilibration
          factors are to be computed. The type of A can be:
          Stype = SLU_NC; Dtype = SLU_D; Mtype = SLU_GE.

  R       (output) double*, size A->nrow
          If INFO = 0 or INFO > M, R contains the row scale factors   
          for A.

  C       (output) double*, size A->ncol
          If INFO = 0,  C contains the column scale factors for A.

  ROWCND  (output) double*
          If INFO = 0 or INFO > M, ROWCND contains the ratio of the   
          smallest R(i) to the largest R(i).  If ROWCND >= 0.1 and   
          AMAX is neither too large nor too small, it is not worth   
          scaling by R.

  COLCND  (output) double*
          If INFO = 0, COLCND contains the ratio of the smallest   
          C(i) to the largest C(i).  If COLCND >= 0.1, it is not   
          worth scaling by C.

  AMAX    (output) double*
          Absolute value of largest matrix element.  If AMAX is very   
          close to overflow or very close to underflow, the matrix   
          should be scaled.

  INFO    (output) int*
          = 0:  successful exit   
          < 0:  if INFO = -i, the i-th argument had an illegal value   
          > 0:  if INFO = i,  and i is   
                <= A->nrow:  the i-th row of A is exactly zero   
                >  A->ncol:  the (i-M)-th column of A is exactly zero   

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