Hot to store results from for loop in matrix

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Sandra Levin 2020-2-7

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/504168-hot-to-store-results-from-for-loop-in-matrix

评论： KSSV 2020-2-7

So,

I'm having trouble storing my results from a for loop in a matrix. I have a 22*9 matrix for which I want to calculate the diffferennce between the columns, for each row. and store it in a new matrix.

I have tried preallocating with zeroes, does not fix the probelm. Something is wring in my code (see below) but I can't seem to figure out what.

What happens is that the output is either (with preallocation) a 22*9 Matrix with only the output of the last calculation in the first and second column of the matrix.

Or, withour preallocation, I get the result as 9 separate vectors, one for each iteration.

very grateful for some input.

Thx!

The code:

for m=1:9
if m==1
    deltaCI=0;
    deltaEA=0;
    deltaP=0;
    
else
    %calculate difference for  CI, EI, EA, between year (column) m and m-1 for each of the 22 rows. 
    deltaCI=CI(:, m)- CI(:, m-1);
    deltaEI=EI(:, m)- EI(:, m-1);
    deltaEA=EA(:, m)- EA(:, m-1);
    deltaP=P(:, m)- P(:, m-1);  
end'
    deltaCI(:,m)=deltaCI
    deltaEI(:,m)=deltaEI
    deltaEA(:,m)=deltaEA
end
resultsco2(:,m)=deltaCI.*deltaEI.*deltaEA.*deltaP;

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EmielH 2020-2-7

在 MATLAB Online 中打开

I think the probleming you're having is caused by the fact that you're overwriting deltaEI deltaEA and deltaP in your if statement. Furthermore I think you can skip the if statement if you let m run from 2:9. Not sure what your code should do or wat CI etc are but I think it should look something like this.

 
deltaCI=zeros(22,9);
deltaEA=zeros(22,9);
deltaP =zeros(22,9);
for m=2:9
    %calculate difference for  CI, EI, EA, between year (column) m and m-1 for each of the 22 rows. 
    deltaCI(:,m)=CI(:, m)- CI(:, m-1);
    deltaEI(:,m)=EI(:, m)- EI(:, m-1);
    deltaEA(:,m)=EA(:, m)- EA(:, m-1);
    deltaP(:,m) =P(:,m)- P(:, m-1);  
end
resultsco2=deltaCI.*deltaEI.*deltaEA.*deltaP;

Sandra Levin 2020-2-7

Thank you! your suggestion did the trick!

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Answer 1

KSSV 2020-2-7

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https://ww2.mathworks.cn/matlabcentral/answers/504168-hot-to-store-results-from-for-loop-in-matrix#answer_414289

编辑：KSSV 2020-2-7

在 MATLAB Online 中打开

You need not to run a loop to get the difference..simply use the fucntion diff.

A = rand(22,9) ; 
A = [zeros(22,1) A] ; 
iwant = diff(A')' ; 

Still, if you want o use the loop. Use like this:

deltaCI = zeros(22,9) ; 
deltaEA = zeros(22,9) ; 
deltaP = zeros(22,9) ; 
for m=2:9
    %calculate difference for  CI, EI, EA, between year (column) m and m-1 for each of the 22 rows. 
    deltaCI(:,m)=CI(:, m)- CI(:, m-1);
    deltaEI(:,m)=EI(:, m)- EI(:, m-1);
    deltaEA(:,m)=EA(:, m)- EA(:, m-1);
    deltaP(:,m)=P(:, m)- P(:, m-1);  
end