Hi Chiel,
As I read the code, fun is defined within the module as Function[fvar,expr]. For this definition to be useful, fvar and expr need to be previously defined such that expr is the expression defining the functional relationship and fvar is a name for a variable which appears in the expression. For that reason, I would expect both values to be defined, probably in the arguments passed to the module. I see that expr is so defined, but fvar is not. This makes me suspect that var appearing as an argument for findRoot should read fvar.
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Kind regards,
David
