As far as I can tell from the output and from a brief perusal of the source, the model is being found infeasible by the pre-solve during the process of tightening bounds. In a nutshell, the solver tries to determine if there are "implied bounds" for any of the variables that are tighter than the ones actually given in the problem description. The logic is that if you have, e.g.,<br>
<br>x1 + x2 <=1<br><br>and x1 and x2 are non-negative variables, then they each have an implied upper bound of 1, even if this is not given as part of the input. You can get implied bounds from the each constraint for each variable and these can be tightened in multiple rounds---one round of tightening leads to further implications in the next round. If the result of this tightening is that the lower bound of a given variable ends up higher than its upper bound, the model is infeasible. As far as I can tell, the number that is being reported there is the number of such violations, but to be honest, this number is very hard to interpret. The single infeasibility could have been caused by any number of the actual linear constraints. <br>
<br>Determining what constraints are causing infeasibility is a difficult problem in general and has been the subject of much research. A good place to start to find out about this area is to put "irreducible inconsistent system" in Google Scholar:<br>
<br><a href="http://goo.gl/qdqyU">http://goo.gl/qdqyU</a><br><br>Cheers,<br><br>Ted<br><br><div class="gmail_quote">On Fri, Aug 10, 2012 at 12:37 PM, Christos <span dir="ltr"><<a href="mailto:chtsolak@gmail.com" target="_blank">chtsolak@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>I forgot to mention that it is a
minimization problem , so i do not know if there is any point in
limiting objective.<br>
<br>
Sorry for the double mail.<div class="im"><br>
<br>
On 10/8/2012 19:24, <a href="mailto:acw@ascent.com" target="_blank">acw@ascent.com</a> wrote:<br>
</div></div><div><div class="h5">
<blockquote type="cite"><font face="sans-serif">No single constraint
is responsible for
an infeasibility. Consider a system with one variable, and two
constraints,
X >= 7 and X <= 4. This system is obviously infeasible,
but
which of the two constraints is at fault?</font>
<br>
<br>
<font face="sans-serif">In your case I suspect that the
problem
is unbounded rather than infeasible, because you have so few
constraints
and so many variables. Unless the problem has a very special
structure,
a problem with fewer constraints than variables is likely to be
unbounded.</font>
<br>
<br>
<font face="sans-serif">You can check this by adding a
constraint
that limits your objective to, say, 1e6. If the problem now
solves,
then unboundedness is almost certainly your difficulty.</font>
<br>
<br>
<br>
<table width="100%">
<tbody>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif" size="1">From:</font>
</td>
<td><font face="sans-serif" size="1">Christos
<a href="mailto:chtsolak@gmail.com" target="_blank"><chtsolak@gmail.com></a></font>
</td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif" size="1">To:</font>
</td>
<td><font face="sans-serif" size="1"><a href="mailto:cbc@list.coin-or.org" target="_blank">cbc@list.coin-or.org</a></font>
</td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif" size="1">Date:</font>
</td>
<td><font face="sans-serif" size="1">08/10/2012 09:32 AM</font>
</td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif" size="1">Subject:</font>
</td>
<td><font face="sans-serif" size="1">[Cbc] Artificial
variables</font></td>
</tr>
</tbody>
</table>
<br>
<hr noshade>
<br>
<br>
<br>
<tt><font>Hi, i have a model with around 10000 variable
and
1500 equations.<br>
<br>
But i get the messages on the photo when i run it:<br>
</font></tt><a href="http://imageshack.us/photo/my-images/39/dascd.png/" target="_blank"><tt><font>http://imageshack.us/photo/my-images/39/dascd.png/</font></tt></a><tt><font><br>
<br>
Is there any way to use artificial variable or something else
in order
<br>
to find the problematic equation?<br>
<br>
Thank you in advance<br>
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</font></tt>
<br>
</blockquote>
<br>
</div></div></div>
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<br></blockquote></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>
<br>