function ran2(idum)
       
         INTEGER idum,IM1,IM2,IMM1,IA1,IA2,IQ1,IQ2,IR1,IR2,NTAB,NDIV
         REAL ran2,AM,EPS,RNMX
		 PARAMETER (IM1=2147483563,IM2=2147483399,AM=1./IM1,IMM1=IM1-1,
     $             IA1=40014,IA2=40692,IQ1=53668,IQ2=52774,IR1=12211,
     $             IR2=3791,NTAB=32,NDIV=1+IMM1/NTAB,EPS=1.2e-7,
     $             RNMX=1.-EPS)
         INTEGER idum2,j,k,iv(NTAB),iy
         SAVE iv,iy,idum2
         DATA idum2/123456789/, iv/NTAB*0/, iy/0/
         
         if (idum.le.0) then
            idum=max(-idum,1)
            idum2=idum
            do j = NTAB+8, 1, -1
               k = idum/IQ1
               idum = IA1*(idum-k*IQ1) - k*IR1
               if (idum.lt.0) idum = idum + IM1
               if (j.le.NTAB)iv(j) = idum
            enddo
            iy = iv(1)
         endif
         k = idum/IQ1
         idum = IA1*(idum - k*IQ1) - k*IR1
         if (idum.lt.0) idum = idum + IM1
         k = idum2/IQ2
         idum2 = IA2*(idum2 - k*IQ2)- k*IR2
         if (idum2.lt.0) idum2 = idum2 + IM2
         j = 1 + iy/NDIV
         iy = iv(j) - idum2
         iv(j) = idum
         if (iy.lt.1) iy = iy + IMM1
         ran2 = min(AM*iy,RNMX)
         return
         
         end