 sharp cut-off filter which sets all values in
the transform of the data in the <b>r</b> array to zero above the
point <b>ncut</b>. Since the filter drops abruptly to zero at
<b>ncut</b>, this results in ringing around the lines, and hence it is
probably not particularly useful.<p>

The second form uses a gaussian filter of width <b>width</b>. This is
often useful to suppress ringing around lines (i.e. the lobes of the
sinc function which appear in the wings of strong lines) caused by
under-resolution. In t