how to extract the diagonal entries out of a matrix

[John W. Eaton]

On  6-Feb-2009, David Doria wrote:

| A = rand(3,3);
| B = diag(A);

Be careful with diag on arbitrary matrices.  If your matrix happens to
sometimes be a vector with more than one element, then diag does
something completely different.  For example, try

  diag (rand (2, 3))
  diag (rand (1, 3))

You can thank Cleve for this (mis)feature.  

jwe