  <span class="Comment">## 		        1 - one-sided derivative (f(x+h) - f(x)  )/h</span>
              <span class="Comment">## 		       -1 - one-sided derivative (f(x)   - f(x-h))/h</span>
              <span class="Comment">## 		        2 - two-sided derivative (f(x+h) - f(x-h))/(2*h)</span>
              <span class="Comment">## 			3 - user-computed analytical derivatives</span>
              <span class="Comment">## </span>
  <span class="Identifier">deriv_debug</span><span class="Operator">*</span><spa