Preallocate variables with unkown size

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Waseem AL Aqqad 2022-5-23

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https://ww2.mathworks.cn/matlabcentral/answers/1724980-preallocate-variables-with-unkown-size

编辑： Waseem AL Aqqad 2022-5-25

I pre allocate the two variables phi and phiPrime by setting a maximum size and then crop them afterwards. The thing is that both of them depend on vector b which changes its size in every ii.

I did something like the following but not sure if it is quite correct and computational effective.

but I'm not sure whether the way I preallocated the variables lead into wrong results or not.

function [G_dmg, G_orig, phic, inActiveSorted] =  SH_decision(G_dmg, G_orig, phic)
N = numnodes(G_dmg); 
inActive = find(degree(G_dmg)==0); 
impact = -1* ones(1,length(inActive)); 
phi = zeros(N, 1); 
phiPrime = zeros(N, 1); 
phidPrime = zeros(N, 1); 
lastIdx = 0;
numNeighborsPernode = []; 
activeNeighbors = []; 
for ii = 1:length(inActive)     
    b = neighbors(G_orig, inActive(ii));
    if ~isempty (b) 
        degreeOrig = degree(G_orig, b); 
        degreeDmg = degree(G_dmg, b); 
        phi(lastIdx + 1: length(b)+lastIdx) = degreeDmg./degreeOrig;  
    
        phiPrime(lastIdx + 1: length(b)+lastIdx) = degreeRestoration./degreeOrig ; 
        
        impact(ii) = nnz(phi(lastIdx + 1: length(b)+lastIdx)<=phi & phiP(lastIdx + 1: length(b)+lastIdx)>phi);
        phidPrime = phiPrime - phi;
        lastIdx = lastIdx + length(b);
        
    end
    
end
phi = phi(1:lastIdx, :);
phiPrime = phiPrime(1:lastIdx, :);
phidPrime = phidPrime(1:lastIdx, :);
end

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KSSV 2022-5-23

Is phi and phiPrime are vectors at the end?

Why you are using (lastIdx + 1: length(b)+lastIdx) as the index while saving inside loop?

Waseem AL Aqqad 2022-5-23

编辑：Waseem AL Aqqad 2022-5-23

Thanks for your reply.

Yes, I'm getting them as vectors.

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采纳的回答

Bruno Luong 2022-5-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1724980-preallocate-variables-with-unkown-size#answer_969570

编辑：Bruno Luong 2022-5-23

在 MATLAB Online 中打开

You can compute exactly the size needed for your vectors

A = G_orig.adjacency;
A(inActive,:) = 0;
m = nnz(A(:,inActive));
phi = zeros(m, 1);
phiPrime = zeros(m, 1);
...

13 个评论
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Bruno Luong 2022-5-25

编辑：Bruno Luong 2022-5-25

If you need it, yes.

Waseem AL Aqqad 2022-5-25

Thanks, Bruno.

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