machine epsilon

SYNOPSIS

#include "matrix.h"
Real  macheps = MACHEPS;

DESCRIPTION

The quantity MACHEPS is a {\tt\#define}'d quantity which is the ``machine epsilon'' or ``unit roundoff'' for a given machine. For more information on this concept, see, e.g., {\sl Introduction to Numerical Analysis\/} by K.\ Atkinson, or {\sl Matrix Computations\/} by G.\ Golub and C.\ Van Loan. The value given is for the standard floating point type Real only. Normally the standard floating point type is double, but in the installation this can be changed to be float or long double. (See the chapter on installation.) For ANSI C implementations, this is set to the value of the DBL_EPSILON or FLT_EPSILON macro defined in .

EXAMPLE

while ( residual > 100*MACHEPS )
{   /* iterate */   }

BUGS

The value of MACHEPS has to be modified in the source whenever moving to another machine if the floating point processing is different.

SOURCE FILE: machine.h