how use equation by custom?

[lab021rnd]

i can't use custom equation? can I know about that.? I want use y = 0.5 * (a * x^3 + b*x^2 +c * x) * z^2
thank you!

[KhaledSharif]

Hi @lab021rnd, thanks for your question! You can define your custom equation similar to how it is done inside Athena, like so:

from athena.equations import get_symbols
def CustomEquation(s, x, x_symbolic, z, z_symbolic):
    offset, variables = 3, 2  # 3 free variables, 2 data-defined variables

    a, b, c = [s.w[s._wc + i] for i in range(offset)]
    syms = get_symbols(1, offset + variables + 1)
    x_s, z_s = syms[-1], syms[-2]

    # this is our TensorFlow equation definition
    eq = 0.5 * (a * x**3 + b*x**2 + c*x) * z**2

    # this is our Sympy equation definition
    equation_string = 0.5 * (syms[0] * x_s**3 + syms[1]*x_s**2 + syms[2]*x_s) * z_s**2

    parameters_list = [[x_symbolic, x_s], [z_symbolic, z_s]] + [[s.w[s._wc + i], syms[i]] for i in range(offset)]

    return {"equation": eq, "parameters": parameters_list, "symbolic": equation_string, "offset": offset}

Then you can call it from inside a model definition, just as you do with any other equation type, as so:

model = AdditiveModel(fw)
model.add(CustomEquation, "x", "z")

This is not very straightforward at the moment, I'll admit, and I hope to work on simplifying this process in the future. Please tell me if this works when you try it out.