First, when you use loops, try to pre-allocate the outcome
N = 1000 ;
p = zeros(N,1) ; % pre-allocation
for k=1:N
p(k) = …
end
Second, matlab can handle matrices at once. You can take advantage of that, rather than going through each element one by one. In your case:
M=rand(5,3,2); % a smaller example
tf = M < 0.5
idx = find(tf) % linear index
[x,y,z] = ind2sub(size(M), idx)
% which can be one-lined into [x,y,z] = ind2sub(size(M), find(tf<0.5))
Now these will give the same result:
R1 = M(tf) ;
R2 = M(idx) ;
R3 = zeros(size(x)) ; % see, pre-allocation again
for k=1:numel(x),
R3(k) = M(x(k),y(k),z(k)) ;
end
disp(R1)
isequal(R1,R2,R3)
