How to avoid using 'for' loop

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moh mor
moh mor 2023-10-22
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.
  1 个评论
moh mor
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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回答（2 个）

Image Analyst
Image Analyst 2023-10-22
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.
  2 个评论
moh mor
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
Image Analyst 2023-10-22
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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Dyuman Joshi
Dyuman Joshi 2023-10-22
Vectorize the function calculateValue() and use sum for calculateValue(u, v, R).
However, this assumes that calculateValue() can be vectorized.
And if it can be, I doubt if you will see any noticeable speed increase by using vectorization instead of using a for loop.
  5 个评论
显示 3更早的评论
moh mor
moh mor 2023-10-22
编辑：Walter Roberson 2023-10-25
As much as I could, I've Vectorized my problem.
Dyuman Joshi
Dyuman Joshi 2023-10-22
编辑：Dyuman Joshi 2023-10-25
@moh mor, is there still a problem?
Does it work properly? And did you check the speed of the two methods for comparison?

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