Paulo answered the question as you phrased it, but if you know the exact number of results you are producing (or if the maximum number of results is "reasonably close" to the likely number of results), then you are better off pre-allocating memory for the results:
a = zeros(10,1);
for b = 1:10
a(b) = 3*b+5; %for example
end
When you get to thousands of elements, pre-allocating can be muchmuch faster.
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