Thanks, the method described works in making evaluations with repeated parameters of the function much faster
StressError[p1_?NumericQ, p2_?NumericQ, p3_?NumericQ, p4_?NumericQ, p5_?NumericQ]:= StressError[p1, p2, p3, p4, p5] = ...
By adding "?NumericQ" I define the function to only evaluate with numeric input (that is how I defined the function initially), so numeric evaluation shouldn't take place.
