function ran1(idum)
		
		  integer idum,IA,IM,IQ,IR,NTAB,NDIV
		  REAL ran1,AM,EPS,RNMX
		  PARAMETER (IA=16807,IM=2147483647,AM=1./IM,IQ=127773,IR=2836,
     $             NTAB=32,NDIV=1+(IM-1)/NTAB,EPS=1.2e-7,RNMX=1.-EPS)		 
          
          INTEGER j,k,iv(NTAB),iy
          DATA iv /NTAB*0/, iy /0/

          if(idum.le.0.or.iy.eq.0) then
             idum=max(-idum,1)
             do j = NTAB+8,1,-1
                k = idum/IQ
                idum = IA*(idum-k*IQ) - IR*k
                if (idum.lt.0) idum = idum+IM
                if (j.le.NTAB) iv(j) = idum
             enddo
             iy = iv(1)
          endif
          k = idum/IQ
          idum = IA*(idum-k*IQ) - IR*k
          if (idum.lt.0) idum = idum+IM
          j = 1 + iy/NDIV
          iy = iv(j)
          iv(j) = idum
          ran1 = min(AM*iy,RNMX)
          
          return
          
       end