HP MLIB User's Guide Vol. 2 7th Ed.

Appendix B 1099

LU factorization DGEFA

ier Status response:

ier = 0 Normal return.

ier = k ≠ 0Ifu

= 0. (u

is the k-th element on

the diagonal of upper triangular

matrix U). Technically, this is not an

error condition for these subprograms,

but it does indicate that A is

computationally singular and that a

division by zero occurs if the

factorization is used to solve a system

of linear equations.

Notes DGEFA is usage compatible with the standard LINPACK subprogram.

The triangular factors are stored in a different format from the format used by

the standard LINPACK subprograms, but are compatible with the VECLIB

subprogram DGESL.

Example Factor the 6-by-6 REAL*8 matrix A stored in array A whose dimensions are

10-by-10.

INTEGER*4 LDA,N,IPVT(10),IER

REAL*8 A(10,10)

LDA = 10

N = 6

CALL DGEFA (A,LDA,N,IPVT,IER)

IF ( IER .NE. 0 ) THEN

handle singular matrix

END IF