le with a nonuniform density.  The spatial region is the unit circle,
      but a nonuniform density is applied to that region.  The density is implicitly defined
      by the sampling routine, which returns many more points near
      the circumference than near the center of the circle.  The result
      is that, during the CVT iteration, the generators arrange themselves
      more densely towards the outer part of the circle.
      <blockquote>
        [ p, t ] = cvt_circle_nonuniform ( n, sample_num, d