function peval,c,x,deriv
;
; Evaluate the polynomial c[0]+c[1]*x+c[2]*x^2+..., or its derivative
;
; B. Knapp, 2000-02-10
;
  n = N_ELEMENTS(c)
  if n_elements( deriv ) eq 0 then deriv=0
;
  y = (x-x)
  for i=n-1,deriv,-1 do begin
     g = c[i]
     for j=0,deriv-1 do g=g*(i-j)
     y = y*x+g
  endfor
  return,y
;
  end