Sum up function handle

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D Frey 2017-12-16

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回答： Daniel Huang 2020-6-3

Hi,

I got a problem with summing up a function handle in a loop. I want that the fuction handle "error" is summed up for all the different "k" in the loop. In this code the function handle "error" and "sum_error" dont change over the loop iterations. "theta" will be in the end a (6,1) vector.

sum_error = zeros(6,1);
for k = 1:N
    error = @(theta)abs(y(k)-phi(k,:)*theta).^2;
    sum_error = @(theta)sum_error + error;
end
x0 = zeros(6,1);
[theta_min,~] = fminsearch(sum_error,x0);

The function handle of error shows in every iteration:

@(theta)abs(y(k)-phi(k,:)*theta).^2

I defined y(k) and phi(k,:). Why is it not inserting this values to the function? And why is the summing up not working?

Thanks for your help!

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Answer 1

YT 2017-12-16

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编辑：YT 2017-12-16

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Although I don't know 'y' and 'phi' (and your 'theta' seems to be constant), I guess it's because you didn't call your 'error' expression with a 'theta' argument

sum_error = sum_error + error(your_theta);

I myself would rewrite it to something like this though (makes it easier I guess)

for  k = 1:N
    sum_error = sum_error + abs(y(k)-phi(k,:)*theta).^2;
end

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D Frey 2017-12-16

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Thanks! I didn't take into account that I have to call 'theta' again. I also used your suggested shorter form. There I also needed to call 'theta' in the sum_error:

for  k = 1:N
    sum_error = sum_error(theta) + abs(y(k)-phi(k,:)*theta).^2;
end

YT 2017-12-16

Glad I could help. Good luck with your project!

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Answer 2

Daniel Huang 2020-6-3

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From my testing in the current version of Matlab, I think it does plug it in but just doesn't show it in the workspace for some reason. I suspect that it saves a "snapshot" of the value of the variable if not referenced as a variable by the function handle. I don't know exactly what's going on, but my testing code that I used to figure this is:

B = @(x)0;
r = [1 2 3 4 5];
test1 = @(x)x.^2;
for ii = 1:5
    B = @(x)test1(x)*r(ii)+B(x);
end

It's weird how the workspace shows the value, but I don't think it's easy to show the actual values for these objects as they are essentially an entire function condensed into one line of code.