SGEFA(3)

SYNOPSIS
SUBROUTINE SGEFA (A, LDA, N, IPVT, INFO)

NAME
sgefa - Factor a matrix using Gaussian elimination.

LIBRARY
SLATEC (LINPACK)

CATEGORY
D2A1

TYPE
SINGLE PRECISION (SGEFA-S, DGEFA-D, CGEFA-C)

KEYWORDS
GENERAL MATRIX, LINEAR ALGEBRA, LINPACK, MATRIX FACTORIZATION

AUTHOR
Moler, C. B., (U. of New Mexico)

DESCRIPTION
SGEFA factors a real matrix by Gaussian elimination. SGEFA is usually called by SGECO, but it can be called directly with a saving in time if RCOND is not needed. (Time for SGECO) = (1 + 9/N)*(Time for SGEFA) . On Entry A REAL(LDA, N) the matrix to be factored. LDA INTEGER the leading dimension of the array A . N INTEGER the order of the matrix A . On Return A an upper triangular matrix and the multipliers which were used to obtain it. The factorization can be written A = L*U , where L is a product of permutation and unit lower triangular matrices and U is upper triangular. IPVT INTEGER(N) an integer vector of pivot indices. INFO INTEGER = 0 normal value. = K if U(K,K) .EQ. 0.0 . This is not an error condition for this subroutine, but it does indicate that SGESL or SGEDI will divide by zero if called. Use RCOND in SGECO for a reliable indication of singularity.

REFERENCES
J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W. Stewart, LINPACK Users' Guide, SIAM, 1979.

ROUTINES CALLED
ISAMAX, SAXPY, SSCAL

REVISION HISTORY (YYMMDD)
780814 DATE WRITTEN
890831 Modified array declarations. (WRB)
890831 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
900326 Removed duplicate information from DESCRIPTION section. (WRB)
920501 Reformatted the REFERENCES section. (WRB)