SRC/cgsequ.c File Reference

Computes row and column scalings. More...

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

Functions
void	cgsequ (SuperMatrix *A, float *r, float *c, float *rowcnd, float *colcnd, float *amax, int *info)
	Driver related.

---

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 CGEEQU
 

---

Function Documentation

void cgsequ	(	SuperMatrix *	A,
		float *	r,
		float *	c,
		float *	rowcnd,
		float *	colcnd,
		float *	amax,
		int *	info
	)

 Purpose   
   =======

   CGSEQU 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_C; Mtype = SLU_GE.

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

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

   ROWCND  (output) float*
           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) float*
           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) float*
           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

   =====================================================================