subroutine fderiv(x,i,a,deltaa,nterms,deriv)
      implicit double precision (a-h,o-z)
      dimension x(50),a(10),deltaa(10),deriv(10)
11    xi=x(i)
      deriv(1)=dexp(a(2)*xi)
      deriv(2)=a(1)*xi*dexp(a(2)*xi)
      deriv(3)=dexp(a(4)*xi)
      deriv(4)=a(3)*xi*dexp(a(4)*xi)
      return
      end