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

## dgsequ()

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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