>

    <p>
      A radial basis interpolant is a useful, but expensive, technique for 
      definining a smooth function which interpolates a set of function values
      specified at an arbitrary set of data points.
    </p>

    <p>
      Given nd multidimensional points xd with function values fd, and a 
      basis function phi(r), the form of the interpolant is
      <pre>
       f(x) = sum ( 1 <= i <= nd ) w(i) * phi(||x-xd(i)||)
      </pre>
      where the weights w have been precomputed by solving