How to Assign a Variable Name to a Point in a Matrix

Question

Sophie Culhane 2020-12-16

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https://ww2.mathworks.cn/matlabcentral/answers/695715-how-to-assign-a-variable-name-to-a-point-in-a-matrix

评论： Ameer Hamza 2020-12-16

I am trying to assign variable name 'centersquare' to the center point in an NRows x NCols matrix. In my program, I had the center calculated every time I went through a for-loop and it worked. However, my professor instructed me to only calculate it once outside of the for-loop to be more efficient. I have tried various things in attempt to only calculate my centersquare once, however it does not work with my program.

Here is what I had before:

for pebbles = 1:NP

A(ceil(NRows/2),ceil(NCols/2)) = A(ceil(NRows/2),ceil(NCols/2)) + 1;

...

end

Here is what I am trying to do:

centersquare = A(ceil(NRows/2),ceil(NCols/2));

for pebbles = 1:NP

centersquare = centersquare + 1;

...

end

Can someone tell me why this isn't working? Thank you

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Answer 1

Ameer Hamza 2020-12-16

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https://ww2.mathworks.cn/matlabcentral/answers/695715-how-to-assign-a-variable-name-to-a-point-in-a-matrix#answer_577440

编辑：Ameer Hamza 2020-12-16

在 MATLAB Online 中打开

I guess your professor asked to pre-calculate the indexes. Something like this

row = ceil(NRows/2);
col = ceil(NCols/2);
for pebbles = 1:NP
    A(row,col) = A(row,col) + 1;
    ...
end

btw, I will be surprised if there is a significant difference. MATLAB JIT compiler is probably intelligent enough to see that the same thing is being used in each iteration. However, this is definitely more readible.