Nested for loop vectorization

Question

Gabriele Dessena 2021-4-1

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/790134-nested-for-loop-vectorization

编辑： Gabriele Dessena 2021-4-1

采纳的回答： Marco Riani

在 MATLAB Online 中打开

Hello everyone,

I am trying to vectorize the creation of this symmetric matrix.

I have tried with meshgrid and ngrid, but I could not find a way to make them work with the way I use X.

Any advice?

Thank you!

X = [1:10; 2:11]';
n = length(X);
theta = .1;
Mat = zeros(n,n);
for i=1:n
    for j=i+1:n
        Mat(i,j)=exp(-sum(theta.*abs(X(i,:)-X(j,:)).^p));
    end
end
Mat = Mat+Mat'+eye(n);

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Answer 1

Marco Riani 2021-4-1

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/790134-nested-for-loop-vectorization#answer_664644

在 MATLAB Online 中打开

% Hi, in your code p is not defined. I assume it is a scalar
% If you want to avoid the loop the answer is
% Mat=exp(-theta*(squareform(pdist(X,'minkowski',p))).^p);
% The code below checks that my implementation gives the same answer as
% your implementation
% Best
% Marco
X = [1:10; 2:11]';
p=3;
n = length(X);
theta = 0.1;
Mat = zeros(n,n);
for i=1:n
    for j=i+1:n
        Mat(i,j)=exp(-sum(theta.*abs(X(i,:)-X(j,:)).^p));
    end
end
Mat = Mat+Mat'+eye(n);
 Matchk=exp(-theta*(squareform(pdist(X,'minkowski',p))).^p);
 disp(max(abs(Mat-Matchk),[],'all'))