modifying one field of defined structure in other used function

Question

Saber 2015-3-12

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https://ww2.mathworks.cn/matlabcentral/answers/182798-modifying-one-field-of-defined-structure-in-other-used-function

评论： Saber 2015-3-12

I have defined a data structure `data` with 7 fields. Two of the fields is as:

    n = 4;
    data = struct();
    data.Aeq = zeros(n);
    data.beq = zeros(n,1);
    m =3;

Now, there is another function `ul(data,m)` that I am passing the `data` and `m` as inputs. Inside `ul()`, I will modify one component of matrix `Aeq` as:

data.Aeq(m,m) = 1;

after running whole the code when I am checking `data.Aeq` it is still zero matrix while I have modified on component. Am I doing something wrong?

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Brendan Hamm 2015-3-12

Please post the function which is supposed to modify the data.

Likely you are trying to use a pass by reference functionality, while MATLAB is pass by value.

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Answer 1

Guillaume 2015-3-12

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As Brendan has stated in his comment, matlab is exclusively pass by value. A function always receive a copy of the input arguments, so modifications are only local to the function.

To solve your problem, modify your function declaration to:

function data = ul(data, m)
   %...body of the function
   data.Aeq(m, m) = 1; %modify local copy which is returned by the function
   %...more code
end

and call your function with:

data = ul(data, m);