<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; "><DIV><DIV>On Mar 7, 2007, at 12:13 PM, Tom Goddard wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"><P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Monaco" size="4" style="font: 14.0px Monaco"><SPAN class="Apple-converted-space"> </SPAN>I didn't understand your explanation of why 4 points are needed for an alignment with the match command.<SPAN class="Apple-converted-space"> </SPAN>It looks like only 3 are needed for a unique match.<SPAN class="Apple-converted-space"> </SPAN>In your example with points ABC and DEF you suggested that the match could either pair A with D, B with E, and C with F or it could pair A with F, B with E, C with D.<SPAN class="Apple-converted-space"> </SPAN>But the match command specifies the desired pairing so only one of those is possible for any match command invocation.</FONT></P> </BLOCKQUOTE><BR></DIV><DIV>Tom's right in that with the correspondences specified, 3 points is enough for a unique superposition. After some investigation, it turns out that back in MidasPlus we used a different superposition algorithm and that algorithm required at least four points to work. Chimera uses a different algorithm -- and there is no minimum! It will work with one point. So the 4-point minimum is an unnecessary restriction and will be removed in future releases (though it will warn about non-uniqueness if you use less than 3 points).</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Navnit, I can send you a file with the restriction removed if you want. Let me know.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>--Eric</DIV><DIV><BR><DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "> Eric Pettersen</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "> UCSF Computer Graphics Lab</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "> <A href="mailto:pett@cgl.ucsf.edu">pett@cgl.ucsf.edu</A></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "> <A href="http://www.cgl.ucsf.edu">http://www.cgl.ucsf.edu</A></DIV></DIV><BR></DIV><DIV><BR class="khtml-block-placeholder"></DIV></BODY></HTML>