I managed to hack the code for problem ns2_8_31.pg (estimate the derivative using an oracle function) from setDerivatives1 of the Rochester library so that I can have students use oracle functions to estimate partial derivatives.
Not knowing Java, I modified the problem to accept two inputs, and then multiplied the two inputs and passed them to the code for the cubic spline already there. It works, but is a hack at best.
My guess is that to do this in a general way would require a bicubic spline numeric process to be written. Can the cubic spline somehow be avoided altogether using MathObjects?
I hate to ask this question because to answer it is probably going to require slugging through some code, but I do love these problems and would like to write some more robust ones. I attached my code as Word document, which has the advantage that I could highlight changes in red.