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For loop in function handle

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Andy Tran
Andy Tran on 24 Jun 2020
Edited: Andy Tran on 28 Jun 2020
I want to creat a function with multiple variables, something like:
f = @(x) = f1(x) + f2(x) + ... + fn(x)
where x is a n-dimensional vector which can be define by user. The number of functions f1,f2,..,fn can be define by user, too.
The question is can i use a for loop in function handle to define f according to the length of vector x?

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Answers (2)

Stephen Cobeldick
Stephen Cobeldick on 24 Jun 2020
Edited: Stephen Cobeldick on 24 Jun 2020
You can simply store function handles in a cell array of any size and use cellfun. No loop required.
>> C = {@sin,@sqrt,@pow2};
>> F = @(x) sum(cellfun(@(f)f(x),C));
>> F(3)
ans = 9.8732
compare with:
>> sin(3) + sqrt(3) + pow2(3)
ans = 9.8732
If you really want to use a for loop then you would need to write the function in an Mfile, e.g.:
function out = myfun(x)
out = 0;
C = {@sin,@sqrt,@pow2};
for k = 1:numel(C)
out = out + C{k}(x);
end
end

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Walter Roberson
Walter Roberson on 27 Jun 2020
You said it yourself, you have an unknown number of variables. The only way to address an indefinite number of variables is to dynamically create the names of the variables and access the contents of the variables through the names you created. Which we firmly advise you not to do.
where p_n are variables.
Don't do that. Instead make p and h into vectors. Then
dot(p, h) - p(n).*h(n)
provided that p(m) and h(m) are finite.
Stephen Cobeldick
Stephen Cobeldick on 28 Jun 2020
"How can i define function C with unknown number of variables (i call it as N), others parameters are generate corresponding to N."
Rather than creating lots of variables the simple and efficient MATLAB way is to use one vector/matrix/array.
Your approach is making this much more complex than it needs to be.
Andy Tran
Andy Tran on 28 Jun 2020
Yes i know it. But further i need to find the maximum of the function C minus D (which is a linear function acording to p_n) for each p_n. The way im trying to do is using anonymous function and so that i think i need to treat p_n as a variable. Do you have other suggestion?
Thanks for helping me out.

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Walter Roberson
Walter Roberson on 26 Jun 2020
The question is can i use a for loop in function handle to define f according to the length of vector x?
NO. Anonymous functions cannot use for .
Anonymous functions can use arrayfun() and cellfun() and can use function calls that process the resulting arrays.

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