How to get a value from inside a function?

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Ana Paula Pagnoncelli 2020-2-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/503994-how-to-get-a-value-from-inside-a-function

回答： Bjorn Gustavsson 2020-2-6

采纳的回答： Bjorn Gustavsson

I'm using the following function in my main program to calculate alpha_def:

alpha_def=fminbnd(@(alpha)fun_a(alpha, data_1, data_2, data_3, data_4, data_5, data_6), -alpha_0, alpha_0, options);

Inside of fun_a, I calculate beta_def the following way:

beta_def=lsqnonlin(@(beta)fun_b(beta, data_3, data_4, data_5, data_6), beta_0)

which is used to calculate alpha_def in fun_a.

After obtaining alpha_def, I need to use the value of beta_def in my main program. Is there a way of getting the value of beta_def from inside fun_a?

Thanks!

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Bjorn Gustavsson 2020-2-6

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No you dont. In your fminbnd call the anonymous function is independent of x and will just give an arbitrary result.

We might assume that you use:

alpha_def=fminbnd(@(x)fun_a(x, data_1, data_2, data_3, data_4, data_5, data_6), -alpha_0, alpha_0, options);

...but it might also be:

alpha_def=fminbnd(@(x)fun_a(alpha, data_1, data_2, data_3, data_4, x, data_6), -alpha_0, alpha_0, options);

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Answer 1

Bjorn Gustavsson 2020-2-6

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https://ww2.mathworks.cn/matlabcentral/answers/503994-how-to-get-a-value-from-inside-a-function#answer_414093

在 MATLAB Online 中打开

So we know something about your functions, but not much more than the most general stuff. If you write your function fun_a something like this:

function varargout = fun_a(alpha,data1,data2,data3,data4,data5,data6,beta_out_too)
beta_0 = alpha-data1; % or something
beta_def=lsqnonlin(@(beta)fun_b(beta, data_3, data_4, data_5, data_6), beta_0);
val = sum((beta_def*alpha-data1./data2).^2);
varargout{1} = val;
if beta_out_too
  varargout{2} = beta_def;
end
end

Then you can change the call to fminbnd to:

alpha_def=fminbnd(@(alpha)fun_a(alpha, data_1, data_2, data_3, data_4, data_5, data_6,0), -alpha_0, alpha_0, options);
% Then call fun_a again to get the beta_def-value you're interested in:
[val,beta_optimal] = fun_a(alpha_def, data_1, data_2, data_3, data_4, data_5, data_6,1);'

HTH