title: generating two orthogonal vectors that are orthogonal to a particular direction
body: <p>What is the simplest and most efficient ways in numpy to generate two orthonormal vectors a and b such that the cross product of the two vectors equals another unit vector k, which is already known?</p>
  
  <p>I know there are infinitely many such pairs, and it doesn't matter to me which pairs I get as long as the conditions axb=k and a.b=0 are satisfied. </p>