title: octave: representing matrices of standard basis vectors
body: <p>Suppose I have a matrix such that each row is a standard basis vector, i.e. each row contains exactly one 1, the other columns being 0.</p>
  
  <p>Is there a convenient way to create such a matrix (i.e. given a vector of positions of where the ones are in each row)?</p>
  
  <p>Also, is there a way I should represent such a matrix so that multiplications with it can be done more efficiently in octave?</p>