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<p>Hello, </p>
<p> I have a weird problem while trying to solve the ampl code using couenne solver. When I tried to minimize it using constraint, <span>X3 = max (0, X1 -2); it gave me the <span>ERROR: unknown operator. But when I used constraint, <span> X3 = max
(0, 9 -2); it gave me the optimal solution. Will you be able to help me with this? I have included the code and the solver output as a reference:-</span></span></span></p>
<p><span><span><br>
</span></span></p>
<div><span style="font-size: 9pt;">var X1 >=0 <=9.5 integer;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">var X2 >=0 <=9.5 integer;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">var X3 >=0 integer;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">minimize Y: -2540.33 -154.669 * X1 + 40.0895 * X2 + X3;</span><br>
</div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);">subject to a1: X3 = max (0, X1 -2); </span><br>
<span style="font-size: 9pt;"></span></div>
<span style="font-size: 9pt;"></span>
<p></p>
<span style="font-size: 9pt;"></span>
<p><br>
<span style="font-size: 9pt;"></span></p>
<span style="font-size: 9pt;"></span>
<p></p>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">ampl: reset;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">ampl: include trial.run;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">couenne: </span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);">ANALYSIS TEST: ERROR: unknown operator (address 0p741f20), aborting.</span></div>
<span style="font-size: 9pt; background-color: rgb(255, 255, 0);"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);">exit code 18446744073709551615</span></div>
<span style="font-size: 9pt; background-color: rgb(255, 255, 0);"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);"><BREAK></span></div>
<div><span style="font-size: 9pt;">*******************************************************************************************************************</span></div>
<div><span style="font-size: 9pt;">var X1 >=0 <=9.5 integer;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">var X2 >=0 <=9.5 integer;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">var X3 >=0 integer;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">minimize Y: -2540.33 -154.669 * X1 + 40.0895 * X2 + X3;</span><br>
</div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);">subject to a1: X3 = max (0, 9 -2); </span><br>
<span style="font-size: 9pt;"></span></div>
<span style="font-size: 9pt;"></span><br>
<span style="font-size: 9pt;"></span>
<p></p>
<span style="font-size: 9pt;"></span>
<p></p>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">ampl: reset;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">ampl: include trial.run;</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">couenne: </span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">ANALYSIS TEST: Problem size before reformulation: 2 variables (2 integer), 0 constraints.</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">Problem size after reformulation: 3 variables (2 integer), 0 constraints.</span></div>
<div><span style="font-size: 9pt;"></span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">******************************************************************************</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">This program contains Ipopt, a library for large-scale nonlinear optimization.</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;"> Ipopt is released as open source code under the Common Public License (CPL).</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;"> For more information visit http://projects.coin-or.org/Ipopt</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">******************************************************************************</span></div>
<div><span style="font-size: 9pt;"></span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;">NOTE: You are using Ipopt by default with the MUMPS linear solver.</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="font-size: 9pt;"> Other linear solvers might be more efficient (see Ipopt documentation).</span></div>
<span style="font-size: 9pt;"></span>
<div><span style="background-color: rgb(255, 255, 0); font-size: 9pt;">Cbc0012I Integer solution of -3925.35 found by Init Rounding NLP after 0 iterations and 0 nodes (0.00 seconds)</span><br>
</div>
<span style="font-size: 9pt; background-color: rgb(255, 255, 0);"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);">Cbc0001I Search completed - best objective -3925.351, took 0 iterations and 0 nodes (0.00 seconds)</span></div>
<span style="font-size: 9pt; background-color: rgb(255, 255, 0);"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);">Cbc0035I Maximum depth 0, 0 variables fixed on redu</span></div>
<span style="font-size: 9pt; background-color: rgb(255, 255, 0);"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);"> </span><span class="Apple-tab-span" style="white-space: pre; font-size: 9pt; background-color: rgb(255, 255, 0);">
</span><span style="font-size: 9pt; background-color: rgb(255, 255, 0);">"Finished"</span></div>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);"></span></div>
<span style="font-size: 9pt; background-color: rgb(255, 255, 0);"></span>
<div><span style="font-size: 9pt; background-color: rgb(255, 255, 0);">couenne: Optima</span><span style="background-color: rgb(255, 255, 0);">l</span></div>
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Thank You.</p>
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<br>
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Regards,</p>
<p class="x_MsoNormal" style="margin:0in 0in 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
Ukesh Chawal</p>
<p class="x_MsoNormal" style="margin:0in 0in 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
Graduate Teaching and Research Assistant</p>
<p class="x_MsoNormal" style="margin:0in 0in 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
IMSE PhD Student</p>
<p class="x_MsoNormal" style="margin:0in 0in 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
The University of Texas at Arlington</p>
<p class="x_MsoNormal" style="margin:0in 0in 0.0001pt; font-size:11pt; font-family:Calibri,sans-serif">
<a href="https://owa.uta.edu/owa/chawalu@exchange.uta.edu/redir.aspx?SURL=KvdqIrJYYFJEInR__ScoZicftjVuRA8fhtn9F2i-SuhixzhS37PSCG0AYQBpAGwAdABvADoAdQBrAGUAcwBoAC4AYwBoAGEAdwBhAGwAQAB1AHQAYQAuAGUAZAB1AA..&URL=mailto%3aukesh.chawal%40uta.edu" id="LPNoLP"><span style="color:blue">ukesh.chawal@mavs.uta.edu</span></a></p>
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