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How can I solve a nonlinear model using Newton Raphson ?

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Mallouli Marwa
Mallouli Marwa on 15 Jul 2019
Commented: Mallouli Marwa on 25 Jan 2020
Hi
How can I solve this nonlinear model using Newton Raphson ?
x1 +x2^2 +cos (x3) = 2
x1 +sin (x2) + x3^3 = 1
x3 +x2^3+x3^3 = 4

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Accepted Answer

Stephan
Stephan on 25 Jan 2020
One way:
result = fsolve(@fun,[1 1 1])
function F = fun(x)
F(1) = x(1) + x(2).^2 + cos(x(3)) - 2;
F(2) = x(1) + sin(x(2)) + x(3).^3 - 1;
F(3) = x(3) +x(2).^3 + x(3).^3 - 4;
end
gives:
Equation solved.
fsolve completed because the vector of function values is near zero
as measured by the value of the function tolerance, and
the problem appears regular as measured by the gradient.
<stopping criteria details>
result =
-0.5583 1.3732 0.8329

  2 Comments

John D'Errico
John D'Errico on 25 Jan 2020
The best way to solve it. Don't use Newton-Raphson at all. :)
Mallouli Marwa
Mallouli Marwa on 25 Jan 2020
If I want to use Newton Raphson.
How can we change it ?

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