<br><font size=2 face="sans-serif">Esben,</font>
<br>
<br><font size=2 face="sans-serif">Yes that is what basisin and out do.
They correspond to INSERT and PUNCH in IBM's MPSX/370 code - you
can tell how long ago that is from "punch". XL meant remove
second variable from basis, set it to lower bound and replace by first
variable. XU to upper bound. There are also UL, LL and BS.</font>
<br>
<br><font size=2 face="sans-serif">Saving and restoring warmstart and solution
should give same result.</font>
<br>
<br><font size=2 face="sans-serif">John</font>
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<td width=40%><font size=1 face="sans-serif"><b>Esben Mose Hansen <esben@ange.dk></b>
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<br><font size=1 face="sans-serif">Sent by: coin-discuss-bounces@list.coin-or.org</font>
<p><font size=1 face="sans-serif">07/19/2007 05:32 AM</font>
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<div align=center><font size=1 face="sans-serif">Please respond to<br>
Discussions about open source software for Operations Research
<coin-discuss@list.coin-or.org></font></div></table>
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<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif">Discussions about open source software
for Operations Research <coin-discuss@list.coin-or.org></font>
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<div align=right><font size=1 face="sans-serif">cc</font></div>
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<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">Re: [Coin-discuss] Warmstart/basis reuse</font></table>
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<br><tt><font size=2>On Wednesday July 18 2007 17:44:03 John J Forrest
wrote:<br>
> Esben,<br>
><br>
> Presolve tries to update basis as it reduces the size of the problem
but<br>
> it does have a much better chance of doing this correctly with the
column<br>
> solution as you suggest. If you start with a basis of full rank
then<br>
> every time a row is removed something has to leave basis - but where
to?<br>
> If the solution value is 7.0 and the removed row puts an upper bound
of<br>
> 7.0 on the variable then it is a good guess to put the variable at
its<br>
> upper bound. Without solution values the code has no idea which
bound to<br>
> put it to.<br>
<br>
Is this what cbc does with BasisIn and BasisOut? Because my collegue made
a <br>
test using these methods and a bunch of similar problems, and there it
worked <br>
well. As far as I can see, BasisOut stores the basis variable, the <br>
correspoding row, and the column solution in that row. It also have some
<br>
flags (XL/XU) which I havn't divined the meaning of yet.<br>
<br>
Thanks for helping :D<br>
<br>
-- <br>
regards, Esben<br>
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