19.7 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];
  endfor
  

  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.