<div dir="ltr"><div>Hi Gregor,</div><div><br></div><div>- The call where the described scenario happens is when calling the CONSEPALP callback. I call my separation routine at CONSEPALP and CONSEPASOL.<br></div><div>- I printed the model in my separation routine using SCIPwriteLP(scip, "test.lp"). Indeed, the knapsack constraint does not appear at that file.</div><div>- SCIPgetLPSolstat(scip) == SCIP_LPSOLSTAT_OPTIMAL returns true</div><div>- I'm querying the variables using SCIPgetSolVal(scip, sol, x[v][i]), where sol is NULL if the routine was called from CONSEPALP.</div><div><br></div><div>Thanks,</div><div>Matheus<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Em ter., 10 de dez. de 2019 às 04:49, Gregor Hendel <<a href="mailto:hendel@zib.de">hendel@zib.de</a>> escreveu:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
Hi Matheus,<br>
<br>
If the constraint flags are set to TRUE, I no longer suspect an
issue with the constraint separation/enforcement order.<br>
<br>
Could you verify that the constraint is contained in the LP using
SCIPwriteLP() in your consenfolp callback? Could you assert that
SCIPgetLPSolstat(scip) == SCIP_LPSOLSTAT_OPTIMAL? Finally, how do
you query the LP solution values of the variables?<br>
<br>
I hope this will help to narrow it down,<br>
Gregor<br>
<br>
<div>Am 09.12.19 um 21:23 schrieb Matheus
Ota:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Hi Gregor,</div>
<div><br>
</div>
<div>My original constraint is flagged with true for the
initial, separate and check parameters. <br>
</div>
<div>Indeed, my constraint handler has a higher priority
(greater than zero, since I want to separate fractional
solutions) than the knapsack constraint handler. So what you
are saying is that I'm calling my callback routine before
adding the knapsack constraints (even though SCIP printed the
knapsack constraint for the transformed model)? Then I guess
this would only happen only once? Because after SCIP adds the
knapsack constraints, all the solutions that enters my
callback will respect the knapsack constraints (**).</div>
<div><br>
</div>
<div>Can I change the separation priority of the knapsack
constraint in the transformed model? This way I guarantee that
the solution that enters my callback already satisfies (**).</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Matheus<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">Em seg., 9 de dez. de 2019 às
13:22, Gregor Hendel <<a href="mailto:hendel@zib.de" target="_blank">hendel@zib.de</a>> escreveu:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div> Hi Matheus,<br>
<br>
your reasoning about negation is correct, so I would expect
that the LP solution satisfies ** at CONSENFOLP. A special
case occurs if the knapsack constraint is flagged by (not
initial/not separate/not check), in which case the
constraint is not immediately part of the root LP and might
not be separated at violation. <br>
<br>
Note that the knapsack constraint handler has a very low
enforcement priority, -600000. Probably, the enforcement
priority of your constraint handler is higher, and the
knapsack constraint handler would add its constraint to the
LP in the same enforcement round, but later?<br>
<br>
Kind regards,<br>
Gregor<br>
<br>
<div>Am 06.12.19 um 01:01 schrieb Matheus Ota:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Hi all,</div>
<div><br>
</div>
<div>First I would like to say that I'm very grateful
for all the help I received from this mailing list! I
have a question regarding a MIP model that I'm
solving. I have some equalities of the following type</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>x_i,0 + x_i,1 == 1, for i = 0, ..., 8 (*)<br>
</div>
</blockquote>
<div><br>
</div>
<div> Thus, SCIP presolve routines replace some of my
variables (x_i,0) by the negation of other variables
(1 - x_i,1). In the transformed model I have only this
constraint</div>
<div>
<p style="margin:0px;text-indent:0px;white-space:pre-wrap"><span style="color:rgb(0,0,0)">
</span></p>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<p style="margin:0px;text-indent:0px;white-space:pre-wrap"><span style="color:rgb(0,0,0)">[knapsack] <R>: +1<~t_x_8,1>[B] +1<~t_x_7,1>[B] +1<~t_x_6,1>[B] +1<~t_x_5,1>[B] +1<~t_x_4,1>[B] +1<~t_x_3,1>[B] +1<~t_x_2,1>[B] +1<~t_x_1,1>[B] +1<~t_x_0,1>[B] <= 4;</span></p>
</blockquote>
<div><br>
</div>
<div> And each variable x is binary. The tilde (~)
means negation here? If so, replacing
<~t_x_i,1> by <t_x_i,0> this would give</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div><t_x_8,0> + ... + <t_x_0,0><= 4
(**)<br>
</div>
</blockquote>
<div><br>
</div>
<div>But at the CONSENFOLP method, SCIP is entering
with a "solution" S with x_i,0 = 1 and x_i,1 = 0,
for i = 0, ..., 8. Which is infeasible because
violates (**). But the SCIP documentation says that
CONSENFOLP is called when an LP solution is
available. But this solution S do not respect the
constraints in my LP. I'm a little confused with
this behavior and would be glad if someone could
give me some light here.</div>
<div><br>
</div>
<div>Thanks!</div>
<div>Matheus<br>
</div>
</div>
</div>
<br>
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