# isqnonlin: compute part of objective function outside of matlab

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SA-W le 11 Août 2022
Commenté : SA-W le 17 Oct 2022
I am solving a partial differential equation depending on some design variables (material parameters). I want to fit the material parameters to the vector of experimental data y using matlabs function isqnonlin.
I am solving the PDE for given material parameters with an external software; the solution vector thus obtained is denoted as s. What I want to minimize is the squared difference between s and y in the l2-norm by using the algorithm implemented in isqnonlin.
Given that I do not compute the PDE solution s in matlab itself, is it possible to use isqnonlin?
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Torsten le 12 Août 2022
And did you already test the data transfer between your PDE solver and MATLAB ?
SA-W le 12 Août 2022
I can transfer data between my PDE solver and MATLAB, that is no problem.

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### Réponse acceptée

Torsten le 12 Août 2022
Modifié(e) : Torsten le 12 Août 2022
Then call "lsqnonlin" as
p0 = ...; % initial guess for the vector of material parameters
sol = lsqnonlin(@(p)fun(p,y),p0)
and write a function "fun" as
function res = fun(p,y)
s = result_from_your_PDE_solver_for_the_vector_of_material_parameters_p_corresponding_to_y(p)
res = s - y;
end
By the way:
The name of the MATLAB function is lsqnonlin (least-squares solver for nonlinear problems), not isqnonlin.