non-linear fit to find constants in the equation

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Baris Gungordu
Baris Gungordu 2019-1-25
评论： Torsten 2019-1-29
I am trying to implement the following equation:
U = C1 + C2*E+ C3*E^2 + C4*E^3 + C5*E^4, where U and E is known (10 set of values , 10 x 2).
I need to get the constants C1 to C5. Tried fitnlm with no success. Looking forward to get your help.
Example data set:
U E
2.019 1.615
2.622 1.662
3.358 1.706
4.36 1.759
5.621 1.814
7.324 1.877
9.379 1.94
12.121 2.011
15.364 2.081
20.101 2.167

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Torsten
Torsten 2019-1-25
E =...; % column vector
U =...; % column vector
A = [ones(numel(E),1), E, E.^2, E.^3, E.^4];
b = U;
sol = A\b;
C1 = sol(1)
C2 = sol(2)
C3 = sol(3)
C4 = sol(4)
C5 = sol(5)
p = [C5 C4 C3 C2 C1];
Usim = polyval(p,E);
plot(E,U,E,Usim)
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Baris Gungordu
Baris Gungordu 2019-1-29
Thanks but it is only returning the initial conditions (p0).
Torsten
Torsten 2019-1-29
Maybe the initial guess p0 is far off. Try to use a better p0-vector.

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