How can I put constraints on individual variables in TemplateExpressionSpec?

[skadoosh-MC]

Hi,

I am using TemplateExpressionSpec to find a specific functional form; however, is it possible to constrain the individual variables within it? For example, I'm doing something like -

template = TemplateExpressionSpec(expressions=['g'],
                                  variable_names=['x1','x2','x3','x4','x5','x6','x7'],
                                  combine='x1 + g(x1, x2, x3, x4, x5, x6, x7)'
)

I would like to put constraints on x1 such that it can only be used with operators like +, -, ×, ÷ and restrict it from appearing as an exponent. I haven't been able to implement this, and any help/suggestions would be very much appreciated.

Note: This may not be relevant, but within my PySRRegressor, I still use some 'global' constraints for the entire equation. I want to put additional constraints on just x1.

PySRRegressor(expression_spec=template,
            binary_operators=["+", "-", "*", "/", "^"],         
            constraints={'^': (-1, 2),
                         '/': (-1, 3)},....)

Thank you in advance : D

[MilesCranmer]

For constraints like this you should take the approach of defining a custom loss_function_expression. I'm on my phone so can't find the others but there are a few similar discussions on the forums. I think for you, you could try to combine some sort of check like violates = any(ex.tree) do node; node.degree == 2 && node.op == 1 && any(node) do subnode; subnode.degree == 0 && !subnode.constant && subnode.feature == 1; end; end, and then increase the loss if violates is true.