problem fitting data to power law

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Jeremy Diallo 2016-3-10

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https://ww2.mathworks.cn/matlabcentral/answers/272615-problem-fitting-data-to-power-law

评论： Are Mjaavatten 2016-3-14

Hi,

I am trying to fit my data to a power law of the form "y =1 - (x/9.5)^n" where n is the parameter to adjust. The data im using for x and y are respectively:

pos_pitot = [-9.5 -8.5 -7.5 -6.5 -5.5 -4.5 -3.5 -2.5 -1.5 -0.5 0.5 1.5 2.5 3.5 4.5 5.5 6.5];
v_sur_vaxe = [0.5611    0.7454    0.8165    0.8498    0.8924    0.9428    0.9718    0.9813    1.0000    1.0000   0.9907    0.9907    0.9718    0.9428    0.9129    0.8819    0.8389];

I tried this code :

fit_curve = fit(pos_pitot', v_sur_vaxe','power2');
r_fit = r/9.5;
plot(r_fit,fit_curve);

I am not even sure this is the right thing to do. Could somebody please help me and provide me a working solution to do this simple adjustement ? This is the first time I am trying to do something like that...

Thanks a lot.

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Star Strider 2016-3-10

I tried to fit your function ‘y = 1 - (x/9.5)^n’ with fminsearch and found that your function produces complex results. You have to sort that before you can fit it successfully.

Are Mjaavatten 2016-3-14

在 MATLAB Online 中打开

Try

plot(v_sur_vaxe,pos_pitot)

This will show you that the the reletionship is not single-valued. pos_pitot seems to depend on another variable in addition to v_sur_vaxe. Have another look at your original problem and see if you can find such a variable. Could both your variables be functions of that one third variable?

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