nest loop

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Dominic Lawson 2011-3-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/4297-nest-loop

采纳的回答： Matt Fig

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Hello,

Here is my code:-

clear all

x = 1:3;

y = 1:3;

a = 1:3;

b = 1:3;

for i = 1:3;

    for j = 1:3;
        a_pred = a(:,i);
        b_pred = b(:,j);
        y_pred = a_pred + b_pred.* x;
        chi2 = (y-y_pred).^2;    
    end

end

how would I amend the nested loop so that every single combination of a and b values are calculated in y_pred please? i.e. a(1) and b(1) then a(2) and b(1) all the way to a(3) and b(3).

Thanks

采纳的回答

Matt Fig 2011-3-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/4297-nest-loop#answer_6012

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Why do you think all aren't being calculated? Here is a modified version of your code, not changing the mechanics, which shows what you are getting.

a = 1:3;
b = 1:3;
for i = 1:3;
    for j = 1:3;
        a_pred = a(:,i);
        b_pred = b(:,j);
        disp([a_pred b_pred])    
    end  
end

EDIT

Here is how to store all the results in chi2:

x = 1:3;
y = 1:3;
a = 1:3;
b = 1:3;
chi2 = zeros(9,3);
cnt = 0;
for i = 1:3;
    for j = 1:3;
        cnt = cnt + 1;
        a_pred = a(:,i);
        b_pred = b(:,j);
        y_pred = a_pred + b_pred.* x
        chi2(cnt,:) = (y-y_pred).^2;
    end  
end
chi2

And here is a vectorized version, using NPERMUTEK:

IDX = npermutek(1:3,2);
y_pred = bsxfun(@plus,a(IDX(:,1)), bsxfun(@times,b(IDX(:,2)),x.'));
chi2 = bsxfun(@minus,y,y_pred.').^2

Not that it should be faster here...

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Walter Roberson 2011-3-29

I found it by using methods(@i)

Walter Roberson 2011-3-29

Good question about 'type'. I was not able to find anything that did not indicate 'simple' there. I did find, though, that functions will use an empty file name for methods that do not have a file of their own. For example, functions(@func2str) where which shows func2str as if it is part of a file that does not actually exist.

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