How to avoid using 'for' loop

Question

moh mor 2023-10-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2036911-how-to-avoid-using-for-loop

编辑： Walter Roberson 2023-10-25

'u' and 'v' are 401*401 matrices and 'R' is a 401*1 matrix. I have a function which gets 'u' and 'v' vectors and one value of 'R' per iteration and calculates the value of the function. Then after that, I have to sum all these values to get the final result. I wish to achieve my goal without using 'for' loop. Is it possible?

Example:

      % Initialize 'u', 'v', and 'R' matrices
      u = ...; % 401x401 matrix
      v = ...; % 401x401 matrix
      R = ...; % 401x1 matrix
      functionValues =zeros(401,401);
      % Calculate the values of the function for each element
      for i=1:numel(R)،
      functionValues = functionValues + calculateValue(u, v, R(i)); % 401x401 matrix
      end

In fact I wish to avoid using 'for' loop to increase running speed.

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moh mor 2023-10-22

Note: 'functionValues' has the same dimension as 'u' and 'v'. In fact I wish to sum up values of 'functionValues' for different 'R' at each position of 'functionValues'.

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Answer 1

Image Analyst 2023-10-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2036911-how-to-avoid-using-for-loop#answer_1338436

Just modify youir calculateValue() so that it takes multiple values of R (can handle R being a vector) and returns a vector instead of a single scalar number. Then just call the function -- no for loop needed.

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moh mor 2023-10-22

Sorry, I think sth is misunderstood. 'functionValues' has the same dimension as 'u' and 'v'. In fact I wish to sum up values of 'functionValues' for different 'R' at each position.

Image Analyst 2023-10-22

在 MATLAB Online 中打开

Then why not

theSum = 0;
for k = 1 : numel(R)،
    theSum = theSum + calculateValue(u, v, R(k)); % 401x401 matrix
end

And I agree with @Dyuman Joshi with only a few iterations (401*401) you'd most likely not notice any difference at all. It might be a different story if you had hundreds of millions of elements.

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