Generally, using find() and growing variables in a loop tend to cause the code to be slower. Here you can replace find() with logical indexing and use preallocation -
nd = [1 0 0 0.36 0; ...
2 0 -0.02 0.33 0; ...
3 0 -0.51 0.33 0; ...
4 0 -0.81 0.33 0; ...
5 0 -0.01 0.33 0; ...
6 0 -0.01 0.33 0; ...
7 0 -0.17 0.33 0; ...
8 0 -0.02 0.33 0; ...
9 0 -0.02 0.33 0; ...
10 0 -0.02 0.33 0];
eld = [1 2; 2 3; 3 4; 4 1; 1 3; 1 2];
n = size(eld,1);
%preallocation
eld2 = zeros(n,2*size(nd,2));
for i=1:n
%remove find
ind1 = ismember(nd(:,1),eld(i,1)); % find index to get the data row from nd variable.
ind2 = ismember(nd(:,1),eld(i,2));
% re-define the "el" variable using the first column of "nd" variable.
eld2(i,:) = [nd(ind1,1:5) nd(ind2,1:5)]; %combine the terms using indexing
end
eld2
There is another approach as well - Vectorization. As MATLAB is optimized for operation involving matrices and vectors, vectorization leads to faster performance in many cases
[~,n1]=ismember(eld(:,1),nd(:,1));
[~,n2]=ismember(eld(:,2),nd(:,1));
n1=nonzeros(n1);
n2=nonzeros(n2);
eld3 = [eld(n1,1) nd(n1,2:end) eld(n2,2) nd(n2,2:end)]
