19.6 Examples

The following are examples of vectorization questions asked by actual users of Octave and their solutions.

• For a vector A, the following loop

            n = length (A);
            B = zeros (n, 2);
            for i = 1:length(A)
              ## this will be two columns, the first is the difference and
              ## the second the mean of the two elements used for the diff.
              B(i,:) = [A(i+1)-A(i), (A(i+1) + A(i))/2)];
            end
  

  can be turned into the following one-liner:

            B = [diff(A)(:), 0.5*(A(1:end-1)+A(2:end))(:)]
  

  Note the usage of colon indexing to flatten an intermediate result into a column vector. This is a common vectorization trick.