Previous: sgbsl Up: ../linpack.html Next: sgedi
SUBROUTINE SGECO(A,LDA,N,IPVT,RCOND,Z)
INTEGER LDA,N,IPVT(1)
REAL A(LDA,1),Z(1)
REAL RCOND
C
C SGECO FACTORS A REAL MATRIX BY GAUSSIAN ELIMINATION
C AND ESTIMATES THE CONDITION OF THE MATRIX.
C
C IF RCOND IS NOT NEEDED, SGEFA IS SLIGHTLY FASTER.
C TO SOLVE A*X = B , FOLLOW SGECO BY SGESL.
C TO COMPUTE INVERSE(A)*C , FOLLOW SGECO BY SGESL.
C TO COMPUTE DETERMINANT(A) , FOLLOW SGECO BY SGEDI.
C TO COMPUTE INVERSE(A) , FOLLOW SGECO BY SGEDI.
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 RCOND REAL
C AN ESTIMATE OF THE RECIPROCAL CONDITION OF A .
C FOR THE SYSTEM A*X = B , RELATIVE PERTURBATIONS
C IN A AND B OF SIZE EPSILON MAY CAUSE
C RELATIVE PERTURBATIONS IN X OF SIZE EPSILON/RCOND
C IF RCOND IS SO SMALL THAT THE LOGICAL EXPRESSION
C 1.0 + RCOND .EQ. 1.0
C IS TRUE, THEN A MAY BE SINGULAR TO WORKING
C PRECISION. IN PARTICULAR, RCOND IS ZERO IF
C EXACT SINGULARITY IS DETECTED OR THE ESTIMATE
C UNDERFLOWS.
C
C Z REAL(N)
C A WORK VECTOR WHOSE CONTENTS ARE USUALLY UNIMPORTANT
C IF A IS CLOSE TO A SINGULAR MATRIX, THEN Z IS
C AN APPROXIMATE NULL VECTOR IN THE SENSE THAT
C NORM(A*Z) = RCOND*NORM(A)*NORM(Z) .
C
C LINPACK. THIS VERSION DATED 08/14/78 .
C CLEVE MOLER, UNIVERSITY OF NEW MEXICO, ARGONNE NATIONAL LAB.
C
C SUBROUTINES AND FUNCTIONS
C
C LINPACK SGEFA
C BLAS SAXPY,SDOT,SSCAL,SASUM
C FORTRAN ABS,AMAX1,SIGN
C