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<div class="moz-cite-prefix">Thank you very much for you time and
your valuable help.<br>
<br>
Yes, all the variables are bounded.. Some of them have equal low
and upper bounds. I tried by differing them, but the problem
remains...<br>
<br>
I would try the option of limiting the objective but the code is
too complex to add a new constrain in a few hours.. (The model is
constructed in C++ by reading an excel file).<br>
<br>
So, i almost agree that the defect is infeasibility.<br>
<br>
Can you suggest any trick to find it while trying to limit the
objective?<br>
<br>
Thank you very much.<br>
<br>
<br>
On 10/8/2012 20:06, <a class="moz-txt-link-abbreviated" href="mailto:acw@ascent.com">acw@ascent.com</a> wrote:<br>
</div>
<blockquote
cite="mid:OFB4DD9712.DF1517EE-ON85257A56.005D5E40-85257A56.005E0B61@ascent.com"
type="cite"><font face="sans-serif" size="2">The objective is a
linear combination of
some set of variables. Of course I don't know what your
objective
function is, but let's call it F.</font>
<br>
<br>
<font face="sans-serif" size="2">Since this is a minimization
problem,
I propose adding one more constraint to the problem, F >=
-1e6. If
unboundedness is the problem, the modified problem will solve
with no trouble.</font>
<br>
<br>
<font face="sans-serif" size="2">In your first response, you
mention
variable bounds. Do you have bounds on all your variables? If
you do, then my analysis is probably wrong and the difficulty is
infeasibility
rather than unboundedness.</font>
<br>
<br>
<font face="sans-serif" size="2">It should not be necessary to
know any
solver internals to figure out what's wrong.</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 class="moz-txt-link-rfc2396E" href="mailto:chtsolak@gmail.com"><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 class="moz-txt-link-abbreviated" href="mailto:acw@ascent.com">acw@ascent.com</a></font>
</td>
</tr>
<tr>
<td valign="top"><font color="#5f5f5f" face="sans-serif"
size="1">Cc:</font>
</td>
<td><font face="sans-serif" size="1"><a class="moz-txt-link-rfc2396E" href="mailto:cbc@list.coin-or.org">"cbc@list.coin-or.org"</a>
<a class="moz-txt-link-rfc2396E" href="mailto:cbc@list.coin-or.org"><cbc@list.coin-or.org></a>,
Allan Wechsler <a class="moz-txt-link-rfc2396E" href="mailto:acw@robson.ascent.com"><acw@robson.ascent.com></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 12:37 PM</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">Re: [Cbc] Artificial
variables</font></td>
</tr>
</tbody>
</table>
<br>
<hr noshade="noshade">
<br>
<br>
<br>
<font size="3">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.<br>
<br>
On 10/8/2012 19:24, </font><a moz-do-not-send="true"
href="mailto:acw@ascent.com"><font color="blue" size="3"><u>acw@ascent.com</u></font></a><font
size="3">
wrote:</font>
<br>
<font face="sans-serif" size="2">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><font
size="3"> <br>
</font><font face="sans-serif" size="2"><br>
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><font size="3">
<br>
</font><font face="sans-serif" size="2"><br>
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><font size="3"> <br>
<br>
</font>
<table width="100%">
<tbody>
<tr valign="top">
<td width="22%"><font color="#5f5f5f" face="sans-serif"
size="1">From:</font><font size="3">
</font>
</td>
<td width="77%"><font face="sans-serif" size="1">Christos </font><a
moz-do-not-send="true" href="mailto:chtsolak@gmail.com"><font
color="blue" face="sans-serif" size="1"><u><chtsolak@gmail.com></u></font></a><font
size="3">
</font>
</td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif" size="1">To:</font><font
size="3">
</font>
</td>
<td><a moz-do-not-send="true"
href="mailto:cbc@list.coin-or.org"><font color="blue"
face="sans-serif" size="1"><u>cbc@list.coin-or.org</u></font></a><font
size="3">
</font>
</td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif" size="1">Date:</font><font
size="3">
</font>
</td>
<td><font face="sans-serif" size="1">08/10/2012 09:32 AM</font><font
size="3">
</font>
</td>
</tr>
<tr valign="top">
<td><font color="#5f5f5f" face="sans-serif" size="1">Subject:</font><font
size="3">
</font>
</td>
<td><font face="sans-serif" size="1">[Cbc] Artificial
variables</font></td>
</tr>
</tbody>
</table>
<br>
<font size="3"><br>
</font>
<hr noshade="noshade"><font size="3"><br>
<br>
</font><tt><font size="2"><br>
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:</font></tt><font
color="blue" size="3"><u><br>
</u></font><a moz-do-not-send="true"
href="http://imageshack.us/photo/my-images/39/dascd.png/"><tt><font
color="blue" size="2"><u>http://imageshack.us/photo/my-images/39/dascd.png/</u></font></tt></a><tt><font
size="2"><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>
_______________________________________________<br>
Cbc mailing list</font></tt><tt><font color="blue" size="2"><u><br>
</u></font></tt><a moz-do-not-send="true"
href="mailto:Cbc@list.coin-or.org"><tt><font color="blue"
size="2"><u>Cbc@list.coin-or.org</u></font></tt></a><font
color="blue" size="3"><u><br>
</u></font><a moz-do-not-send="true"
href="http://list.coin-or.org/mailman/listinfo/cbc"><tt><font
color="blue" size="2"><u>http://list.coin-or.org/mailman/listinfo/cbc</u></font></tt></a><font
size="3"><br>
</font>
<br>
<br>
</blockquote>
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