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Discrepancy between normal computations and the "subs" function results.

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MDL
MDL el 13 de Sept. de 2023
Comentada: Dyuman Joshi el 13 de Sept. de 2023
I'm dealing with quadratic equations, so i have something like:
k1 * x1^2 + k2 * x2^2 (quadratic terms) + k3 * x1 * x2 (mixed term) + k4 * x1 + k5 * x2 (linear terms) + k6 (constant)
Note: the equations im dealing with are way more complicated, they have more quadratic, mixed and linear terms. Im just simplifying the equation to explain the problem.
I know both the coefficients (k1, k2, ..., k6) and the unknown parameters (x1, x2). So i just have to substitue these values in the equation and get the result.
The problem is this:
If i use the "subs" function (result = subs(equation, x, unknown_parameters_values) i get one result. Note that "equation" is a symbolic function of course.
If i compute the products and sum them i get another result, which differs a lot from the one i get from using the "subs" function.
I know it is an apporximation problem, but is there a way I can fix it? Also what result is more accurate, the first one where i use the "subs" function or the one where i compute the terms one by one? I would like to get at least 2 similar results.
Thank you for your help.
  5 comentarios
Matt J
Matt J el 13 de Sept. de 2023
Editada: Matt J el 13 de Sept. de 2023
which differs a lot from the one i get from using the "subs" function.
Please also elaborate on "differs a lot". What is the relative error?
Dyuman Joshi
Dyuman Joshi el 13 de Sept. de 2023
@MDL Please attach the code you are working with or relevenat portion of it.

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