Reply To: species gradient calculation UDF error — can’t find the function

[Rob]

More that if the data doesn't exist until after an iteration/time step when you try and use the nonexistent data that could trigger the crash. If you're saving gradients & have them calculated you should have something to then Execute on Demand. 

I'd use the TUI command over the Scheme one, mainly as I'd need to look up what the rp-command was doing. That's also an rpgetvar so should tell you what's set, and not change anything.