>
<dd><p>optional values defining the x and y radii of the weighting ellipse.
If not supplied, these are calculated as the span of x
and y over the square root of the number of data.</p></dd>


<dt id="arg-gamma">gamma<a class="anchor" aria-label="anchor" href="#arg-gamma"></a></dt>
<dd><p>grid-focussing parameter.  At each successive iteration, <code>xr</code> and
<code>yr</code> are reduced by a factor of <code>sqrt(gamma)</code>.</p></dd>


<dt id="arg-iterations">iterations<a class="anchor" aria-label="