HP 42S Question

[lrdheat]

I use a neat program for finding extremums by solving to find when d/dx=0. The derivative program goes like this

LBL "DX"
MVAR "X"
MVAR "H"
RCL "X"
RCL "H"
COMPLEX
XEQ "FX"
COMPLEX
END

This works in solve for most routine functions ("FX"). I am having a problem with a more complicated function, where the program for the function ("FX") executes successfully, but my derivative function ("DX") will not work in solve (generates an "invalid type" error).

An example is the following program "(FX") which executes successfully, but not in the solver in program "DX"

LBL "FX"
ENTER
ENTER
ENTER
X^2
5
-
X<0?
+/-
SQRT
END

Is there a way to handle this sort of thing where the DX program can work in solve?