ContourPlot, etc.: not every point a Real

*To*: mathgroup at smc.vnet.net*Subject*: [mg87453] ContourPlot, etc.: not every point a Real*From*: Will Robertson <wspr81 at gmail.com>*Date*: Fri, 11 Apr 2008 01:41:52 -0400 (EDT)

Hello, I just discovered something a little strange and hoped someone here might be able to shed some light on the matter. (I'm using Mathematica 6.0.1.) Take this following code. It defines a function and uses it in a contour plot; the trick is that every value is intercepted on the way through (I use this in ColorbarPlot to extract max/min values): fn := #1^3 + #2^2 & everyNonReal = {}; Eval[x__] := Module[{val = Evaluate@fn@x}, If[Head@val =!= Real, AppendTo[everyNonReal, val]]; val] ContourPlot[Eval[x, y], {x, -2, 2}, {y, -2, 2}] Union@everyNonReal If every evaluation of fn resulted in a Real (as I would expect), then the output should be {} as the if statement would never evaluate. But there's a point in there that's *not* being evaluated, as you can see. What's going on? Working around this problem results in an extra If statement for every single evaluated point, a state of affairs I'm not so fond of. Many thanks, Will