THE EGS5 CODE SYSTEM

interiors of the intervals. If FEXACT(IFUN,J) and FFIT(IFUN,J) are the exact and fitted values of
the IFUN th component at E(J), then the flow of the logical function QFIT may be shown as follows:
LOGICAL FUNCTION QFIT(NINT)
(commons and declarations)
QFIT=.TRUE.
REM=0.0
NI=10*NINT
DO J=1,NI
DO IFUN=1,NFUN
AER=ABS(FEXACT(IFUN,J)-FFIT(IFUN,J))
AF=ABS(FEXACT(IFUN,J))
IF(AF.GE.ZTHR(IFUN)) THEN
IF(AF.NE.0.0) REM=AMAX1(REM,AER/AF)
ELSE
IF(AER.GT.ZEP(IFUN)) QFIT=.FALSE.
END DO
END DO
QFIT=QFIT.AND.REM.LE.EP
RETURN
END
Thus we see that EP is the largest allowed relative error for those points where the absolute computed
value is above ZTHR(IFUN), and ZEP(IFUN) is the largest allowed absolute error for those points
where the absolute computed value is less than ZTHR(IFUN).
Other features of the QFIT routine include provisions for aligning a subinterval boundary at a
specified point in the overall interval (in case the fitted function has a discontinuous slope such as
at the pair production or Møller thresholds), and computing fit parameters in bins flanking the
main interval to guard against truncation errors in sub-interval index computations.
The net result of the fit is the determination of coefficients AX, BX, AF(IFUN,J), and BF(IFUN,J)
such that
FVALUE(E)=AF(IFUN,INTERV)*XFUN(E) + BF(IFUN,INTERV)
is the value of the IFUN th function, and where
INTERV=INT(AX*XFUN(E) + BX).
XFUN is called the distribution function and is ln(E − RM) for electrons and ln(E) for photons.
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