factln.f90

FORTRANvisualfortran常用数值算法集及源码

FUNCTION factln(n)
INTEGER n
REAL factln
!USES gammln
REAL a(100),gammln
SAVE a
DATA a/100*-1./
if (n<0) pause 'negative factorial in factln'
if (n<=99) then
  if (a(n+1)<0.) a(n+1)=gammln(n+1.)
  factln=a(n+1)
else
  factln=gammln(n+1.)
endif
END FUNCTION factln