gammln.f90

FORTRANvisualfortran常用数值算法集及源码

FUNCTION gammln(xx)
REAL gammln,xx
INTEGER j
DOUBLE PRECISION ser,stp,tmp,x,y,cof(6)
SAVE cof,stp
DATA cof,stp/76.18009172947146d0,-86.50532032941677d0,&
     24.01409824083091d0,-1.231739572450155d0,&
	 .1208650973866179d-2,-.5395239384953d-5,&
	 2.5066282746310005d0/
x=xx
y=x
tmp=x+5.5d0
tmp=(x+0.5d0)*log(tmp)-tmp
ser=1.000000000190015d0
do j=1,6
  y=y+1.d0
  ser=ser+cof(j)/y
end do
gammln=tmp+log(stp*ser/x)
END FUNCTION gammln