fun(@x)

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aymos 2018-6-26

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评论： Walter Roberson 2021-2-27

Hi,

I have a semilog graph which must be fitted (in its linear region) using this equation: y = 6e17*B*log[(x+B)/B]

Can you please tell how can I obtain the value of constant B, using fun(@x) ?

Thank you so much in advance for your help !

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Rik 2018-6-26

You should look into the fit function.

aymos 2018-6-26

Can you please be more elaborate ?

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回答（2 个）

Ameer Hamza 2018-6-26

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编辑：Ameer Hamza 2018-6-26

在 MATLAB Online 中打开

If you have a vector of x and y values then you can use several functions to estimate B. The correct method to use depending on your definition of the error function. For example, if you want to estimate B by minimizing the MSE (mean square error) then use lsqcurvefit(). For example,

xdata = ...; % vector of x values
ydata = ...; % vector of y values
y = @(B, x) 6e17*B.*log((x+B)./B);
B_estmated = lsqcurvefit(y, 1, xdata, ydata);
                            ^ initial point for the numerical optimization algorithm.

Similarly, if you have some other error function, then you can use fmincon().

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aymos 2018-6-27

Thanks Ameer.. and by what variable are you defining the predicted output ? (you are using y for both predicted and actual output?)

[~, y] = ode45(@(t,y) odefun(A, B, C, y), t, y0);

Ameer Hamza 2018-6-27

Yes, this equation will give the predicted output y. Also, I realize that using one y together in one statement can be a bit confusing but this syntax is correct. MATLAB does not confuse both y's with each other. You can change either one of the y to another variable name to avoid confusion.

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