function fchisq(y,sigmay,npts,nfree,mode,yfit)
      implicit double precision (a-h,o-z)
      dimension y(100),sigmay(100),yfit(100)
11    chisq=0.
12    if (nfree) 13,13,20
13    fchisq=0.
      goto 40
20    do 30 i=1,npts
21    if (mode) 22,27,29
22    if (y(i)) 25,27,23
23    weight=1./y(i)
      goto 30
25    weight=1./(-y(i))
      goto 30
27    weight=1.
      goto 30
29    weight=1./sigmay(i)**2
30    chisq=chisq+weight*(y(i)-yfit(i))**2
31    free=nfree
32    fchisq=chisq/free
40    return
      end