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Dear Veronica,<br>
<br>
equality constraints should be fine.<br>
<br>
Can you check which constraints are in the LP and which not (and in
particular that there are no additional cuts in the LP). For a
linear constraint, you get the information by getting the row via
SCIPgetRowLinear() and then calling SCIProwIsInLP().<br>
<br>
Additionally, you could send me the log of your run, perhaps I can
see something in there (best with printing statistics in the end).<br>
<br>
Best,<br>
Gerald<br>
<br>
<div class="moz-cite-prefix">Am 05.03.2015 um 12:25 schrieb Veronica
Dal Sasso:<br>
</div>
<blockquote
cite="mid:CABefrmS33TGum0s3V19KRLGWy8Oxj0gHDvO1TLRAM8dyAaq9bQ@mail.gmail.com"
type="cite">
<div dir="ltr">Good morning and thank you for the reply.
<div>1) yes, it is solved to optimality</div>
<div>2) I have only linear constraints, but some of them are
equality constraints. Can this be a problem?</div>
<div>3) actually, <span style="font-size:12.8000001907349px">SCIPgetNConss(scip)
and SCIPgetNLPRows() are different. In particular, in my
test instance they are different both if I use presolve (</span><span
style="font-size:12.8000001907349px">SCIPgetNConss(scip) = </span><span
style="font-size:12.8000001907349px">SCIPgetNLPRows() +3)
and if I disable it </span><span
style="font-size:12.8000001907349px">(</span><span
style="font-size:12.8000001907349px">SCIPgetNConss(scip) = </span><span
style="font-size:12.8000001907349px">SCIPgetNLPRows() +1)</span></div>
<div><span style="font-size:12.8000001907349px"><br>
</span></div>
<div><span style="font-size:12.8000001907349px">Always for the
test instance, at the end, the dual LP objective is twice
the primal objective.</span></div>
<div><span style="font-size:12.8000001907349px">Thanks for your
help,</span></div>
<div><span style="font-size:12.8000001907349px">Veronica</span></div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2015-03-04 19:18 GMT+01:00 Gerald
Gamrath <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:gamrath@zib.de" target="_blank">gamrath@zib.de</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF"> Dear Veronica,<br>
<br>
sorry for the late reply, but we were quite busy in the
last weeks.<br>
<br>
Your understanding of the dual variables is correct, they
should lead to the same objective value as the primal LP
solution (at least of the LP was solved to optimality).
Actually, the dual LP solution should even be dual
feasible.<br>
<br>
Could you please check:<br>
1) that the LP was solved to optimality
(SCIPgetLPSolstat() == SCIP_LPSOLSTAT_OPTIMAL)<br>
2) check that you have only linear constraints and that
those have only one side (SCIPgetRhsLinear() is infinity
or SCIPgetLhsLinear() is -infinity)<br>
3) make sure that there are no additional rows
(SCIPgetNConss(scip) == SCIPgetNLPRows())<br>
<br>
How big is the difference between the primal and the dual
LP objective that you computed?<br>
<br>
Best,<br>
Gerald<br>
<br>
<div>Am 19.02.2015 um 11:13 schrieb Veronica Dal Sasso:<br>
</div>
<div>
<div class="h5">
<blockquote type="cite">
<div dir="ltr">Good morning,
<div>thank you for your reply but no, my variables
are simply non-negative. </div>
<div>Best regards,</div>
<div>Veronica Dal Sasso</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2015-02-18 16:49
GMT+01:00 Ambros Gleixner <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:gleixner@zib.de"
target="_blank">gleixner@zib.de</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0
0 0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">Hi Veronica,<br>
<br>
If you have nonzero bounds on your variables
then you need to consider their reduced
costs. Might that be the case?<br>
<br>
Best regards,<br>
Ambros<br>
<br>
<br>
Am 18.02.2015 um 16:25 schrieb Veronica Dal
Sasso:<br>
<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px
#ccc solid;padding-left:1ex">
<div>
<div> Hello everyone.<br>
I'm not sure about the use of the
function SCIPgetDualsolLinear(). I'm<br>
trying to solve a linear program using
column generation, and at each<br>
iteration I get the values of the dual
variables using<br>
SCIPgetDualsolLinear(scip, cons). I
expect these dual variables to be<br>
the ones that satisfy the complementary
slackness conditions and that,<br>
if I compute the dual objective
function, give the same value as for the<br>
primal objective function but gives an
unfeasible solution to the dual<br>
problem. Instead, I find that the dual
optimal objective function has<br>
not the same value. Is it possible that
I misunderstood the meaning of<br>
SCIPgetDualsolLinear() or simply I'm
making some sort of error that I<br>
haven't found yet in the computing of
the dual objective function's value?<br>
Thank you in advance,<br>
Veronica Dal Sasso<br>
<br>
<br>
</div>
</div>
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<span><font color="#888888"> </font></span></blockquote>
<span><font color="#888888"> <br>
-- <br>
______________________________________________________________<br>
Ambros M. Gleixner<br>
Zuse Institute Berlin - TU Berlin - Berlin
Mathematical School<br>
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