Hi all,<br><br>There have been a number of reports of Clp failing to solve very simple LPs. The below was posted to the SYMPHONY mailing list, but since the problem in question is an LP and is not pre-processed by SYMPHONY, this seems to be a problem with Clp. I am looking into it, but I thought I would throw it onto the Clp list in case anyone else is seeing the same thing or wants to help.<br>
<br>Cheers,<br><br>Ted<br><br><div class="gmail_quote">---------- Forwarded message ----------<br>From: <b class="gmail_sendername">Federico Larumbe</b> <span dir="ltr"><<a href="mailto:federico.larumbe@polymtl.ca">federico.larumbe@polymtl.ca</a>></span><br>
Date: Thu, Jul 19, 2012 at 4:46 PM<br>Subject: [Symphony] Incorrect solution for a simple linear programming model<br>To: <a href="mailto:symphony@list.coin-or.org">symphony@list.coin-or.org</a><br><br><br>Hi,
<div><br></div><div>I am testing Symphony with a simple example in AMPL format:</div><div><div><font face="'courier new', monospace"><br></font></div><div><font face="'courier new', monospace"><div>symphony -F file.mod -D file.dat</div>
</font></div><div><font face="'courier new', monospace"><br></font></div></div><blockquote style="margin:0 0 0 40px;border:none;padding:0px"><div><div><span style="font-family:'courier new',monospace">-- file.mod ------</span><span style="font-family:'courier new',monospace">------------</span></div>
</div><div><div><font face="'courier new', monospace">var y >= 0;</font></div></div><div><div><font face="'courier new', monospace"><br></font></div></div><div><div><font face="'courier new', monospace">minimize ObjectiveFunction: y;</font></div>
</div><div><div><font face="'courier new', monospace"><br></font></div></div><div><div><font face="'courier new', monospace">subject to C1: y >= 1.0;</font></div></div><div><div><font face="'courier new', monospace">subject to C2: y <= 2.0;</font></div>
</div><div><div><font face="'courier new', monospace">subject to C3: y = 1.1;</font></div></div><div><div><font face="'courier new', monospace"><br></font></div></div><div><div><font face="'courier new', monospace">end;</font></div>
</div><div><span style="font-family:'courier new',monospace">------------------</span><span style="font-family:'courier new',monospace">------------</span></div><div><span style="font-family:'courier new',monospace"><br>
</span></div><div><div><span style="font-family:'courier new',monospace">-- file.dat ------</span><span style="font-family:'courier new',monospace">------------</span></div></div><div><span style="font-family:'courier new',monospace">data;</span></div>
<div><span style="font-family:'courier new',monospace">end;</span></div><div><div><span style="font-family:'courier new',monospace">------------------</span><span style="font-family:'courier new',monospace">------------</span></div>
</div></blockquote><div><span style="font-family:'courier new',monospace"><br></span></div><div><font face="arial, helvetica, sans-serif">The solution given by the program is 2.0 instead of 1.1 (see attached file). If I choose maximize, the solution is 1.0. If I remove C3, the problem is unbounded. Is there any option that I missing?</font></div>
<div><font face="arial, helvetica, sans-serif"><br></font></div><div><font face="arial, helvetica, sans-serif">I compiled Sympthony in SUSE Linux with gcc 4.5.1 with the following commands:</font></div><div><font face="arial, helvetica, sans-serif"><br>
</font></div><blockquote style="margin:0 0 0 40px;border:none;padding:0px"><div><font face="'courier new', monospace">./configure --with-gmpl --enable-openm</font></div><div><font face="'courier new', monospace">make</font></div>
</blockquote><div><font face="arial, helvetica, sans-serif"><br></font></div><div><font face="arial, helvetica, sans-serif">Thanks a lot,</font></div><div><font face="arial, helvetica, sans-serif">Federico.</font></div><span class="HOEnZb"><font color="#888888"><div>
<br></div>-- <br>Federico Larumbe<br>École Polytechnique de Montréal<br>Montréal H3C 3A9<br><br>Group for Research in Decision Analysis (GERAD)<br>tel <a href="tel:%2B1%20514%203406053%20xt%206931" value="+15143406053" target="_blank">+1 514 3406053 xt 6931</a><br>
fax <a href="tel:%2B1%20514%203405665" value="+15143405665" target="_blank">+1 514 3405665</a><br>
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<br></div><br><br clear="all"><br>-- <br>Dr. Ted Ralphs<br>Associate Professor, Lehigh University<br>(610) 628-1280<br>ted 'at' lehigh 'dot' edu<br><a href="http://coral.ie.lehigh.edu/%7Eted" target="_blank">coral.ie.lehigh.edu/~ted</a><br>
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