sgefa.f
SUBROUTINE SGEFA (A, LDA, N, IPVT, INFO)
C***BEGIN PROLOGUE SGEFA
C***PURPOSE Factor a matrix using Gaussian elimination.
C***LIBRARY SLATEC (LINPACK)
C***CATEGORY D2A1
C***TYPE SINGLE PRECISION (SGEFA-S, DGEFA-D, CGEFA-C)
C***KEYWORDS GENERAL MATRIX, LINEAR ALGEBRA, LINPACK,
C MATRIX FACTORIZATION
C***AUTHOR Moler, C. B., (U. of New Mexico)
C***DESCRIPTION
C
C SGEFA factors a real matrix by Gaussian elimination.
C
C SGEFA is usually called by SGECO, but it can be called
C directly with a saving in time if RCOND is not needed.
C (Time for SGECO) = (1 + 9/N)*(Time for SGEFA) .
C
C On Entry
C
C A REAL(LDA, N)
C the matrix to be factored.
C
C LDA INTEGER
C the leading dimension of the array A .
C
C N INTEGER
C the order of the matrix A .
C
C On Return
C
C A an upper triangular matrix and the multipliers
C which were used to obtain it.
C The factorization can be written A = L*U , where
C L is a product of permutation and unit lower
C triangular matrices and U is upper triangular.
C
C IPVT INTEGER(N)
C an integer vector of pivot indices.
C
C INFO INTEGER
C = 0 normal value.
C = K if U(K,K) .EQ. 0.0 . This is not an error
C condition for this subroutine, but it does
C indicate that SGESL or SGEDI will divide by zero
C if called. Use RCOND in SGECO for a reliable
C indication of singularity.
C
C***REFERENCES J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W.
C Stewart, LINPACK Users' Guide, SIAM, 1979.
C***ROUTINES CALLED ISAMAX, SAXPY, SSCAL
C***REVISION HISTORY (YYMMDD)
C 780814 DATE WRITTEN
C 890831 Modified array declarations. (WRB)
C 890831 REVISION DATE from Version 3.2
C 891214 Prologue converted to Version 4.0 format. (BAB)
C 900326 Removed duplicate information from DESCRIPTION section.
C (WRB)
C 920501 Reformatted the REFERENCES section. (WRB)
C***END PROLOGUE SGEFA