<div dir="ltr"><div><div>Hi Gerald,<br>
<br>
<span lang="en"><span>thanks</span>
<span>for the quick response. <br>
<br>
</span></span>
<span lang="en"><span>We are
working on the separation of zerohalf cuts in branch-and-price
and we want to implement this in GCG. Therefore, we extended
SCIP's zerohalf separator. At the moment we store for each
zerohalf cut </span></span><span lang="en"><span><span lang="en"><span>the corresponding coefficients of
the lprows which were used to create the zerohalf cut. We
want to use this information in the pricing problem in
order to include the zerohalf cuts correctly in the
branch-price-and-cut procedure. <br>
<br>
The problem is that in GCG we only calculate a variable's
coefficients corresponding to the constraints and not to
the rows </span></span></span></span><span lang="en"><span><span lang="en"><span>of the
master problem. </span></span></span></span><span lang="en"><span><span lang="en"><span>This is
why it would be helpful to have the constraints
corresponding to the rows that were used to create a
zerohalf cut. But maybe we can access this information by
using SCIPgetRowLinear() and getting the corresponding
coefficient of the row. If our problem only contains
linear constraints (which it does since the master problem
in GCG only constains linear constraints), each row
corresponds to one linear constraint and this should work. Do you agree with that?<br><br></span></span></span></span></div><span lang="en"><span><span lang="en"><span>Regards,<br></span></span></span></span></div>
<span lang="en"><span><span lang="en"><span>Markus<br></span></span></span></span></div><div class="gmail_extra"><br><br><div class="gmail_quote">2014-04-01 9:06 GMT+02:00 Gerald Gamrath <span dir="ltr"><<a 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 Markus,<br>
<br>
there is no such method in SCIP. The reason for this is, that in a
general CIP setting, there is no one-to-one correspondence between
constraints and rows. An "and" constraint, for example can add
multiple rows to get a tighter relaxation of the constraint in the
LP. The knapsack constraint handler, on the other hand, separates
knapsack cover cuts, so generates multiple rows as well, even if the
initial LP relaxation is just one row. Even more, a constraint
handler could also separate cuts based on more than one constraint
of its type.<br>
<br>
Therefore, there is no general method for this. "<a>SCIPgetRowLinear</a>" is implemented in the
linear constraint handler, which knows at that point that it creates
exactly one row for each constraint and therefore can return the
row.<br>
<br>
What was it you wanted to do? Perhaps you can just work on the row
(you can get the columns there and also get the variable for a
column by "SCIPcolGetVar") or work directly on the linear
constraints?<br>
<br>
Best,<br>
Gerald<br>
<br>
<div>Am <a href="tel:31.03.2014%2019" value="+13103201419" target="_blank">31.03.2014 19</a>:13, schrieb Markus
Kruber:<br>
</div>
<blockquote type="cite"><div><div class="h5">
<div dir="ltr">
<div>
<div>Dear all,<br>
<br>
</div>
I have given a row in my LP which belongs to a linear
constraint. Now I am looking for a method which returns me
this linear constraint. <br>
I already have found the method "<a>SCIPgetRowLinear</a>".
In my understanding the other direction.<br>
</div>
<div><br>
</div>
<div>Best regards,<br>
</div>
Markus</div>
<br>
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