  The code is by Greg von Winckel.
    </p>

    <p>
      The original version of this software is available at the Matlab Central File Exchange:
      <a href = "http://www.mathworks.com/matlabcentral/fileexchange/19063-sparse-grid-quadrature/content/spquad.m">
                 http://www.mathworks.com/matlabcentral/fileexchange/19063-sparse-grid-quadrature/content/spquad.m</a>.
    </p>

    <p>
      Note that the <b>spquad()</b> function, by default, assumes that the integration region
      is [-1,+1]