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Dear Ahmed,<br>
<br>
yes, it is a normal behaviour you can observe on many MIQCPs. During
presolving SCIP detects some structures which can be reformulated
with the help of auxiliary variables. For example, one can replace
the product of binary variables by using an AND constraint, or
disaggregate quadratic constraints into smaller ones, ...<br>
<br>
In the log file you can see that because of these reformulations
(and probably other presolving techniques) SCIP was able to reduce
the number of quadratic constraints a lot. It might be worth to test
different values for the parameters<br>
<br>
constraints/quadratic/disaggregate<br>
constraints/quadratic/replacebinaryprod<br>
<br>
in the quadratic constraint handler to have more control over the
applied reformulations.<br>
<br>
<br>
Cheers,<br>
<br>
Benny<br>
<br>
<br>
<div class="moz-cite-prefix">On 03/10/2016 04:53 AM, Ahmed Ibrahim
wrote:<br>
</div>
<blockquote
cite="mid:7BE9AA462EB7354CAA5256EB22A6A0DCB8AE09BA@UMCE3EXMD01.ad.umanitoba.ca"
type="cite">
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<div style="direction: ltr;font-family: Tahoma;color:
#000000;font-size: 10pt;">Hi All,
<div>I was wondering whether it is normal for the presolver to
return a presolved MIQCP with a larger number of continuous
variables and larger number of linear constraints than was
provided in the original instance?</div>
<div>The details are provided below (N.B iam using opti toolbox
which interfaces SCIP with Matlab):</div>
<div>
<div> Problem Properties: </div>
<div># Decision Variables: <span style="background-color:
rgb(255, 255, 0);">527</span></div>
<div># Constraints: 4261</div>
<div> # Linear Inequality: <span
style="background-color: rgb(255, 255, 0);">
256</span></div>
<div> # Quadratic Constraints: 2844</div>
<div> # Bounds: 1054</div>
<div> # Binary Variables: 107</div>
<div>------------------------------------------------------</div>
<div> Solver Parameters:</div>
<div>Solver: SCIP</div>
<div>------------------------------------------------------</div>
<div>numerics/lpfeastol = 1e-012</div>
<div>feasible solution found by trivial heuristic after 0.0
seconds, objective value -1.000000e+000</div>
<div>presolving:</div>
<div>(round 1, fast) 9 del vars, 20 del conss, 0 add
conss, 0 chg bounds, 0 chg sides, 0 chg coeffs, 0 upgd
conss, 0 impls, 42 clqs</div>
<div>(round 2, fast) 9 del vars, 20 del conss, 7560 add
conss, 0 chg bounds, 0 chg sides, 0 chg coeffs, 840 upgd
conss, 0 impls, 42 clqs</div>
<div>(round 3, fast) 9 del vars, 20 del conss, 7560 add
conss, 0 chg bounds, 840 chg sides, 840 chg coeffs, 840 upgd
conss, 2520 impls, 760 clqs</div>
<div>(round 4, exhaustive) 9 del vars, 20 del conss, 7560 add
conss, 0 chg bounds, 840 chg sides, 840 chg coeffs, 1074
upgd conss, 2520 impls, 760 clqs</div>
<div>(round 5, medium) 9 del vars, 22 del conss, 7644 add
conss, 0 chg bounds, 840 chg sides, 840 chg coeffs, 1074
upgd conss, 2604 impls, 844 clqs</div>
<div>(round 6, exhaustive) 9 del vars, 108 del conss, 7646 add
conss, 0 chg bounds, 840 chg sides, 840 chg coeffs, 1074
upgd conss, 2604 impls, 844 clqs</div>
<div>(round 7, exhaustive) 9 del vars, 108 del conss, 7646 add
conss, 0 chg bounds, 840 chg sides, 1917 chg coeffs, 1074
upgd conss, 2604 impls, 844 clqs</div>
<div> (0.2s) probing: 51/106 (48.1) - 0 fixings, 0
aggregations, 0 implications, 0 bound changes</div>
<div> (0.2s) probing aborted: 50/50 successive totally
useless probings</div>
<div>presolving (8 rounds: 8 fast, 5 medium, 4 exhaustive):</div>
<div> 9 deleted vars, 108 deleted constraints, 7646 added
constraints, 0 tightened bounds, 0 added holes, 840 changed
sides, 1917 changed coefficients</div>
<div> 2604 implications, 867 cliques</div>
<div>presolved problem has 3038 variables (106 bin, 0 int, 0
impl, <span style="background-color: rgb(255, 255, 0);">
2932 cont</span>) and 10638 constraints</div>
<div> <span style="background-color: rgb(255, 255, 0);">2604
constraints of type <varbound></span></div>
<div> 42 constraints of type <setppc></div>
<div> 2 constraints of type <and></div>
<div> <span style="background-color: rgb(255, 255, 0);"> 5882
constraints of type <linear></span></div>
<div> 104 constraints of type <logicor></div>
<div> 2004 constraints of type <quadratic></div>
</div>
<div><br>
</div>
<div><br>
</div>
<div>Regards,</div>
<div>Ahmed</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
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</blockquote>
<br>
<pre class="moz-signature" cols="72">--
______________________________
Benjamin Müller
Zuse Institute Berlin
Takustr. 7, 14195 Berlin
<a class="moz-txt-link-abbreviated" href="mailto:benjamin.mueller@zib.de">benjamin.mueller@zib.de</a>
+49 30 841 85-195</pre>
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