subroutine dftop1(x,gprob,dfprob,mxg,
     +                  mx,nx,dx,x1,x2)
c     This routine bilinearly interpolates dfprob to
c     the point x for each group. This is the 1-D version
c     of dftop.  
c 
      dimension dfprob(0:mx,mxg),gprob(mxg)
c
      xlocal = x
      if (xlocal .lt. x1) xlocal = x1
      if (xlocal .gt. x2) xlocal = x2
c
      do m=1,mxg
         gprob(m) = 0.0
      enddo
c
c     Calculate indices of left point closest to (x)
      ix = ifix((xlocal-x1)/dx)
c
      if (ix .lt.    0) ix = 0
      if (ix .gt. nx-1) ix = nx-1
c
      xn = (xlocal-x1)/dx - float(ix)
c
c     write(6,*) 'dx: ',dx
c     write(6,*) 'x1: ',x1
c     write(6,*) 'ix: ',ix
c     write(6,*) 'xn: ',xn
c
      do m=1,mxg
         g00 = dfprob(ix  ,m)
         g10 = dfprob(ix+1,m)
c
         a = g00
         b = g10 - g00
c
         gprob(m) = a + b*xn 
      enddo
c
      return
      end