SuperLU  5.0
Functions
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

– 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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