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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=PT link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>John,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Regarding the other thread (assertion failure), your fix seems to work, thanks.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>I have unearthed this week-old thread because we came across a different situation where CBC reports infeasibility, even though the problem is indeed feasible. See files here:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>https://drive.google.com/open?id=0B-5kPpSmX5imVllVaUdxVWY3TGc<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Breaking it down:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span lang=EN-GB style='font-size:11.0pt;font-family:Symbol;color:#1F497D;mso-fareast-language:EN-US'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-GB style='font-size:11.0pt;font-family:Consolas;color:#1F497D;mso-fareast-language:EN-US'>cbc -import test.lp -mipstart ms.before.txt<o:p></o:p></span></p><p class=MsoNormal style='margin-left:35.4pt'><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Reports infeasibility.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span lang=EN-GB style='font-size:11.0pt;font-family:Symbol;color:#1F497D;mso-fareast-language:EN-US'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-GB style='font-size:11.0pt;font-family:Consolas;color:#1F497D;mso-fareast-language:EN-US'>cbc -import test.lp -mipstart ms.txt<o:p></o:p></span></p><p class=MsoNormal style='margin-left:35.4pt'><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Solves problem to optimality, but rejects MIP start.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>The files ms.txt and ms.before.txt have exactly the same solution.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>We traced the issue to this constraint:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:Consolas;color:#1F497D;mso-fareast-language:EN-US'> __one = 1<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>If we remove it, the .before MIP start is accepted and the model is solved to optimality.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>In this particular case, we can do without the </span><span lang=EN-GB style='font-size:11.0pt;font-family:Consolas;color:#1F497D;mso-fareast-language:EN-US'>__one</span><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'> var, but in the general case we add it because it is sometimes convenient for us to pass a constant term in the objective function.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Can you take a look at it?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Rúdi Araújo.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'> John Forrest [mailto:john.forrest@fastercoin.com] <br><b>Sent:</b> quinta-feira, 5 de janeiro de 2017 15:29<br><b>To:</b> Rudi Araújo <rudi.araujo@siscog.pt><br><b>Cc:</b> 'Tiago Maduro Dias' <tiago@siscog.pt>; 'Luís Borges de Oliveira' <lbo@siscog.pt><br><b>Subject:</b> Re: CBC rejecting its own solution as MIP start<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Rudi,<br><br>On 04/01/17 17:39, Rudi Araújo wrote:<br>> <o:p></o:p></p><p class=MsoNormal>> John,<o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>> Thank you the fast reply.<o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>> The .before hint did the trick for the LP I sent you. However, we<o:p></o:p></p><p class=MsoNormal>> came across a different situation where the mipstart is accepted but<o:p></o:p></p><p class=MsoNormal>> CBC reports infeasibility and exits without finding an integer<o:p></o:p></p><p class=MsoNormal>> solution, even though it exists:<o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>><br>That was more interesting - a bug which was unlikely to occur in normal use, but could. As the code had a cutoff value, it added that as a constraint in preprocessing and there was a bug there.<br> <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>> By the way, what is the reason for building the initial solution only<o:p></o:p></p><p class=MsoNormal>> after pre-processing by default? Would it make sense to do it the<o:p></o:p></p><p class=MsoNormal>> other way around - by default before, with an option to do it only<o:p></o:p></p><p class=MsoNormal>> after?<o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>I did not write that bit of code and don't really want to do too much to it. Some information which could get used in heuristics can not easily be passed across when creating solution before - so on the whole it is more efficient to try and do work on preprocessed problem.<br>> <o:p></o:p></p><p class=MsoNormal>> One last thing: trunk appears to be broken. We tried compiling it and<o:p></o:p></p><p class=MsoNormal>> tripped over this error:<o:p></o:p></p><p class=MsoNormal>> <o:p></o:p></p><p class=MsoNormal>><br>My error (you picked it up before I was told off this morning after standard Coin builds were done). I am doing some development in trunk and thought I might as well commit some extra changes instead of taking them out temporarily. However I forgot that I would also need to commit changes from CoinUtils.<br> <o:p></o:p></p><p class=MsoNormal>John Forrest<o:p></o:p></p></div></body></html>