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<p class=MsoNormal><span lang=DE>Dear CLP users,<o:p></o:p></span></p>
<p class=MsoNormal><span lang=DE><o:p> </o:p></span></p>
<p class=MsoNormal>I have a problem using the pivot method correctly. Basically,
I try to find out how I can decide a priori if a pivot step is possible or not
instead of stumbling over the assert that fabs(alpha_)>1e-12.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Given the outgoing variable in sequenceOut_, ClpSimplex::pivot
seems to use the pivotVariable_ array to to find the pivot element. Apparently
I could check pivotVariable_ before calling pivot() to find the pivot element. Additionally,
I'd have to check the value of the pivot element alpha_. It seems to me that
the value of alpha_ is the result of the factorization done in <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New"'>factorization_->updateColumnFT(rowArray_[2],rowArray_[1])</span><o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Without doing this factorization I cannot decide if the
pivot can be done or not. Am I correct? Should I do this calculation beforehand
to implement a test? Since the pivot() function already exists, I thought there
must be a way to do what I am trying to do that is conformant with the OSI
interface, am I right?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I'd appreciate any help in this matter.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks in advance,<o:p></o:p></p>
<p class=MsoNormal>Sebastian<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Some more background information on what I am trying to
achieve: <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I'm trying to solve LP problems that are highly degenerate. Thus,
my optimal primal basis contains slack variables with value 0. As far as I
understand, this basic slack variable can be made non-basic and another slack
variable can be made basic in its place without changing the values of basic
non-slack variables. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I'd like to pivot out each basic slack variable with value
0. I would like to pivot in a non-basic slack variable instead. For now, any
non-basic slack variable would do. In the end, I would prefer to pivot in a non-basic
slack variable that leads to a different dual solution. The goal is to
enumerate (possibly all) dual solutions that belong to the same primal
solution. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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<!--[object_id=#0342cca8cd3ef743bdaeaa37dbcc7c82#]--><P style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma,Verdana,Arial">--<BR>Sebastian Theophil (<A href="mailto:stheophil@think-cell.com">stheophil@think-cell.com</A>)<BR>Software Engineer </P><!--[object_id=#think-cell.com#]--><TABLE style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma,Verdana,Arial" cellSpacing=0>
<TBODY>
<TR>
<TD style="PADDING-RIGHT: 10pt">think-cell Software GmbH</TD>
<TD colSpan=2><A href="http://www.think-cell.com/">http://www.think-cell.com</A></TD></TR>
<TR>
<TD style="PADDING-RIGHT: 10pt">Invalidenstr. 34</TD>
<TD style="PADDING-RIGHT: 5pt">phone</TD>
<TD>+49-30-666473-10</TD></TR>
<TR style="HEIGHT: 20pt" vAlign=top>
<TD style="PADDING-RIGHT: 10pt">10115 Berlin, Germany</TD>
<TD style="PADDING-RIGHT: 5pt">toll-free (US)</TD>
<TD>+1-800-891-8091</TD></TR>
<TR>
<TD colSpan=3>Directors: Dr. Markus Hannebauer, Dr. Arno Schoedl</TD></TR>
<TR>
<TD colSpan=3>Amtsgericht Charlottenburg, HRB 85229</TD></TR></TBODY></TABLE></body>
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