There are some limitations on what kind of values and operations we support. To give an example, it’s impossible to have floating-point inputs or outputs (though you can still use them, see Working With Floating Points — Concrete Numpy Manual). If you are getting this error when you try to compile a function, it means the function is not compilable right now. Also don’t forget to have a look to Numpy Support — Concrete Numpy Manual. Please submit an issue so that we become aware of your use case (see Debugging / Support / Submitting Issues — Concrete Numpy Manual for further details).