<div>hello,</div> <div> </div> <div>I am using OsiClp to extract extreme points/rays of a certain polyhedron by solving a linear program. When the linear program is unbounded, the extreme rays returned by OsiClp have very large coefficients which creates numerical difficulties. Scaling these extreme rays is one option, but it doesn't seem to work well too. Sample code to reproduce the problem is available at,</div> <div> </div> <div><SPAN id=lw_1174096500_0 style="BACKGROUND: none transparent scroll repeat 0% 0%; BORDER-BOTTOM: #0066cc 1px dashed">http://www.andrew.cmu.edu/user/anureets/tmp/primalRay.tgz</SPAN><BR></div> <div>I was wondering if anyone has used OsiClp to extract extreme rays and knows some simple trick to get around this problem. I have tried putting off the presolve options but with little help.</div> <div> </div> <div>Interestingly, I had raised this issue a few months back (email attached). Since being able to extract extreme
rays/points is one of the fundamental advantages of using a simplex procedure, it will be very nice if we could fix this deficiency in OsiClp.</div> <div> </div> <div>regards & thanks,</div> <div>Anureet Saxena</div> <div> </div> <div>Earlier email (oct 2006): </div> <div>hi,<BR><BR>I am trying to use OsiClpSolverInterface::getPrimalRay(const int) to extract<BR>extreme rays of a certain unbounded linear program. I have two questions and<BR>would really appreciate if someone could help me with these: <BR><BR>1. The primal rays returned by getPrimalRay() are double arrays with very large<BR>numbers. Even for a very simple linear program with 2 variables and one<BR>constraint the extreme ray seems to have numbers of the order of 10^8. A very<BR>simple example and code to illustrate this is available at:<BR><BR><SPAN id=lw_1174096500_0 style="BACKGROUND: none transparent scroll repeat 0% 0%; BORDER-BOTTOM: #0066cc 1px
dashed">http://www.andrew.cmu.edu/user/anureets/tmp/primalRay.tgz</SPAN><BR><BR>As I understand, OsiClp is performing some kind of persolve analysis which<BR>leads to this behaviour. <BR><BR>a. Is it possibe to instruct the presolver to return "neat" extreme rays?<BR>b. Is it possible to turn off this presolve analysis? <BR><BR>2. The argument to getPrimalRays(const int) seems redundant since the code<BR>anyway returns only one extreme ray (This is also the case with OsiCpx).<BR><BR>regards,<BR>anureet<BR><BR><BR><BR></div><BR><BR>Anureet Saxena<br> anureet@cmu.edu<br> anureet@yahoo.com<br> <br>--This mail was delivered to you on 100% recyclable electrons.<p> 
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