This sounds like a good idea. Does your sdiffgrad extension handle mixed derivatives such as diff(gamma_incomplete(a^2,x^42),a,2,x) OK? Barton -----maxima-bounces at math.utexas.edu wrote: ----- >1.?Allow?a?lambda?expression?to?define?a?derivative. >2.?Allow?the?value?NIL,?when?we?do?not?know?the?derivative.