gamma.F

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C************************************************************************
      FUNCTION gamma(XX)
      REAL gammagammln,xx
      INTEGER j
      REAL ser,stp,tmp,x,y,cof(6)
      SAVE cof,stp
      DATA cof,stp/76.18009172947146e0,-86.50532032941677e0,
     & 24.01409824083091e0,-1.231739572450155e0,.1208650973866179e-2,
     & -.5395239384953e-5,2.5066282746310005e0/
      x=xx
      y=x
      tmp=x+5.5e0
      tmp=(x+0.5e0)*log(tmp)-tmp
      ser=1.000000000190015e0
      DO j=1,6
         y=y+1.e0
         ser=ser+cof(j)/y
      ENDDO
      gammln=tmp+log(stp*ser/x)
      gamma = exp(gammln)
      RETURN
      END