[Coin-lpsolver] getPrimalRay()
John J Forrest
jjforre at us.ibm.com
Wed Oct 25 11:03:18 EDT 2006
Anureet,
You can set the hint OsiDoPresolveInInitial to false to switch off
presolve.
I am quite happy to add code to scale down ray in simple cases but this
may affect existing code. If I did it would be to scale down largest
until smallest element is as far from one e.g. smallest 1.0e-5, largest
1.0e-5. It gets more complicated when largest is 1.0e12 and smallest is
1.0e-15. Obviously the user can do their own scaling.
I can do whatever people want.
John Forrest
Anureet Saxena <anureet at yahoo.com>
Sent by: coin-lpsolver-bounces at list.coin-or.org
10/25/2006 02:02 AM
To
coin-lpsolver at list.coin-or.org, anureet at cmu.edu, anureet at yahoo.com
cc
Subject
[Coin-lpsolver] getPrimalRay()
hi,
I am trying to use OsiClpSolverInterface::getPrimalRay(const int) to
extract
extreme rays of a certain unbounded linear program. I have two questions
and
would really appreciate if someone could help me with these:
1. The primal rays returned by getPrimalRay() are double arrays with very
large
numbers. Even for a very simple linear program with 2 variables and one
constraint the extreme ray seems to have numbers of the order of 10^8. A
very
simple example and code to illustrate this is available at:
http://www.andrew.cmu.edu/user/anureets/tmp/primalRay.tgz
As I understand, OsiClp is performing some kind of persolve analysis which
leads to this behaviour.
a. Is it possibe to instruct the presolver to return "neat" extreme rays?
b. Is it possible to turn off this presolve analysis?
2. The argument to getPrimalRays(const int) seems redundant since the code
anyway returns only one extreme ray (This is also the case with OsiCpx).
regards,
anureet
Anureet Saxena
anureet at cmu.edu
anureet at yahoo.com
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