Preallocate variables with unkown size

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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
  2 Comments
Waseem AL Aqqad
Waseem AL Aqqad on 23 May 2022
Thanks for your reply.
Yes, I'm getting them as vectors.

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Accepted Answer

Bruno Luong
Bruno Luong on 23 May 2022
Edited: Bruno Luong on 23 May 2022
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);
...
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