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<div class="moz-cite-prefix"><font color="#990000">A lot of very
useful info in one email! -many explanatory questions arise!<br>
<br>
Look under your sentences.</font><br>
<br>
<br>
<br>
On 10/8/2012 23:10, <a class="moz-txt-link-abbreviated" href="mailto:acw@ascent.com">acw@ascent.com</a> wrote:<br>
</div>
<blockquote
cite="mid:OF567A977D.D09D53D7-ON85257A56.006DF072-85257A56.006EDCE1@ascent.com"
type="cite"><font face="sans-serif" size="2">The problem is
certainly infeasibility.
Unboundedness is simply not possible if all the variables have
bounds.
Here are some random ideas.</font>
<br>
<br>
<font face="sans-serif" size="2">If you can do it without
modifying your
code too painfully, you might try selectively disabling
constraints to
find an infeasible set.</font>
<br>
<br>
</blockquote>
<font color="#990000">Because it is painful, i will try the other
solutions first.</font><br>
<blockquote
cite="mid:OF567A977D.D09D53D7-ON85257A56.006DF072-85257A56.006EDCE1@ascent.com"
type="cite"><font face="sans-serif" size="2">I assume you have
some integer variables.
If so, make sure that their bounds all include at least one
integer.
For instance, if X is an integer, but 0.3 <= X <= 0.82,
then
the problem is infeasible because there are no integers in that
range.</font>
<br>
<br>
</blockquote>
<font color="#990000">I do not understand what do you mean "integer
variables" as soon as i do not declare anywhere, i only pass the
column and row bounds, the objective, the value, index, start
matrices, and the number of rows and columns.<br>
<br>
But there are no such bound in any of the variables. Some have
equal bounds (0), i do not know if this is a problem. I doesn't
seems to be..<br>
</font><br>
<blockquote
cite="mid:OF567A977D.D09D53D7-ON85257A56.006DF072-85257A56.006EDCE1@ascent.com"
type="cite"><font face="sans-serif" size="2">Look at your
objective, and try removing
the lower bounds on some variables with positive coefficients,
or the upper
bounds on some with negative coefficients. This might give you
a
better idea of the nature of the infeasibility.</font>
<br>
</blockquote>
<font color="#990000">All variables have positive coefficients and
all have collb=0. I made them -infinity but the defect became
bigger</font><br>
<blockquote
cite="mid:OF567A977D.D09D53D7-ON85257A56.006DF072-85257A56.006EDCE1@ascent.com"
type="cite">
<br>
<font face="sans-serif" size="2">Remember that an infeasibility is
a
distributed issue; you cannot attribute it to a single bound or
constraint.
The best you can hope for is to find a small subset of your
bounds
and constraints that is still infeasible, but is simple enough
to understand.</font>
<br>
<br>
<font face="sans-serif" size="2">You might want to try saving the
problem
as an MPS file (using WriteMps), so that you can more easily
modify the
problem and make your debug cycle simpler.</font>
<br>
<br>
</blockquote>
<font color="#990000">This would be really useful. How can i use it
through C++? <br>
As i mentioned C++ reads data from excel file, puts them in
matrices, builds the model (ie the index, value, start, obj...)
and calls the solver.<br>
How can i make it write an .mps file? Do i need time to learn
something like CBC?<br>
<br>
Thank you<br>
</font><br>
<blockquote
cite="mid:OF567A977D.D09D53D7-ON85257A56.006DF072-85257A56.006EDCE1@ascent.com"
type="cite">
<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">Allan Wechsler
<a class="moz-txt-link-rfc2396E" href="mailto:acw@robson.ascent.com"><acw@robson.ascent.com></a>,
<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></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 03:59 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">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, </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">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><font size="3"> <br>
</font><font face="sans-serif" size="2"><br>
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><font
size="3"> <br>
</font><font face="sans-serif" size="2"><br>
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><font size="3">
<br>
</font><font face="sans-serif" size="2"><br>
It should not be necessary to know any solver internals to
figure out what's
wrong.</font><font size="3"> <br>
<br>
</font>
<table width="100%">
<tbody>
<tr valign="top">
<td width="9%"><font color="#5f5f5f" face="sans-serif"
size="1">From:</font><font size="3">
</font>
</td>
<td width="90%"><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:acw@ascent.com"><font
color="blue" face="sans-serif" size="1"><u>acw@ascent.com</u></font></a><font
size="3">
</font>
</td>
</tr>
<tr>
<td valign="top"><font color="#5f5f5f" face="sans-serif"
size="1">Cc:</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
face="sans-serif" size="1">
</font><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
face="sans-serif" size="1">,
Allan Wechsler </font><a moz-do-not-send="true"
href="mailto:acw@robson.ascent.com"><font color="blue"
face="sans-serif" size="1"><u><acw@robson.ascent.com></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 12:37 PM</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">Re: [Cbc] Artificial
variables</font></td>
</tr>
</tbody>
</table>
<br>
<font size="3"><br>
</font>
<hr noshade="noshade"><font size="3"><br>
<br>
<br>
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><font face="sans-serif" size="2"><br>
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"> </font><font
face="sans-serif" size="2"><br>
<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">
</font><font face="sans-serif" size="2"><br>
<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>
</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>
<br>
</font>
<hr noshade="noshade"><font size="3"><br>
</font><tt><font size="2"><br>
<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><font color="blue" size="3"><u><br>
</u></font><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>
<br>
</font>
<br>
<br>
</blockquote>
<br>
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