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<p>Dear SCIP and Soplex community,</p>
<p><br>
</p>
<p>I face 2 problems using Soplex.</p>
<p><br>
</p>
<p><u>Problem 1</u></p>
<p>I am working on solving a problem in lp format with 2240 variables in [0,1] and 60467 constraints and an objective function of max 0. The first problem I face would be the difference in solving time of Soplex, using the command line versus reading the file
from a C++ code.</p>
<p><br>
</p>
<p>Let us call the file problem.lp.</p>
<p>Doing ./soplex -x problem.lp takes only 3s,</p>
<p><br>
</p>
<p>while doing</p>
<p><br>
</p>
<p><span>auto t_befsolve = high_resolution_clock::now();</span><br>
</p>
<p></p>
<div>SoPlex mysoplex;</div>
<div>mysoplex.readFile("problem.lp", 0, 0, 0);</div>
<span>stat = mysoplex.optimize();</span><br>
<p></p>
<p><span></span></p>
<div>auto t_aftsolve = high_resolution_clock::now();</div>
<div>duration<double> solving_time = t_aftsolve - t_befsolve;</div>
<div><br>
</div>
<div>in a C++ code takes 20s to solve the same problem.</div>
<div><br>
</div>
<div>I have tried both the <span>SOLVEMODE_RATIONAL and the default solving mode, both don't differ significantly in time.</span></div>
<div><br>
</div>
<div>Would anybody be able to advice what to do for this problem?</div>
<div><br>
</div>
<div><u>Problem 2</u></div>
<div>The second problem I face would be different solutions to the same problem using Soplex. In this case, I am working on solving a problem with 2240 variables in {0,1} and 60467 constraints with an objective function of max 0. I wrote a program to convert
this problem to lp format internally with 2240 variables in [0,1] and 60467 constraints and used Soplex's functions to represent the problem in the form of a soplex object.</div>
<div><br>
</div>
<div><span>Doing</span></div>
<div><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px">SoPlex mysoplex</span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px">;</span><br>
</span></div>
<div><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px"><br>
</span></span></div>
<div><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px">(Code to convert initial problem to lp)</span></span></div>
<div><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px"><br>
</span></span></div>
<div><span>mysoplex.writeFileReal("testingreal.lp", NULL, NULL, NULL); gives exactly the same representation as problem.lp above in Problem 1, aside from the constraints looking like </span><br>
</div>
<div><span><span>C0 : -1.0000000000000000e+00 x0 >= 0.0000000000000000e+00</span><br>
</span></div>
<div><span><span>instead of</span></span></div>
<div><span><span>- x0 >= 1</span></span></div>
However, when I try to solve this problem using
<p></p>
<p><span><span>stat = mysoplex.optimize();</span></span></p>
<p><span><span>, and print the solution, I obtain a different solution from Problem 1, which is strange. This also takes around 20s.</span></span></p>
<p><span><span><br>
</span></span></p>
<p><span><span>However, when I use the command line to do</span></span></p>
<p><span><span>./soplex -x testingreal.lp</span></span></p>
<p><span><span>, I obtain the same solution as</span></span></p>
<p><span><span>./soplex -x problem.lp</span></span></p>
<p><span><span>, where this is supposed to be the case. Doing this takes 3s for each lp file.</span></span></p>
<p><span><span><br>
</span></span></p>
<p><span><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px">Would anybody be able to advice what to do for this problem?</span><br>
</span></span></p>
<p><span><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px"><br>
</span></span></span></p>
<p><span><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px">Thank you all very much for helping me to think about these problems.
Any suggestions would be greatly appreciated.</span></span></span></p>
<p><span><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px"><br>
</span></span></span></p>
<p><span><span><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px">Yours sincerely,</span></span></span></p>
<p>Chia Teck Yan</p>
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