187 lines
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187 lines
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<a href="#nested-classes">Classes</a> |
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<a href="#namespaces">Namespaces</a> |
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<a href="#func-members">Functions</a> </div>
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<div class="headertitle"><div class="title">linear_expr.h File Reference</div></div>
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</div><!--header-->
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<div class="contents">
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
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<div class="textblock"><p >This file allows you to write natural code (like a mathematical equation) to model optimization problems with MPSolver. </p>
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<p >It is syntatic sugar on top of the MPSolver API, it provides no additional functionality. Use of these APIs makes it much easier to write code that is both simple and big-O optimal for creating your model, at the cost of some additional constant factor overhead. If model creation is a bottleneck in your problem, consider using the MPSolver API directly instead.</p>
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<p >This file contains two classes:</p><ol type="1">
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<li>LinearExpr: models offset + sum_{i in S} a_i*x_i for decision var x_i,</li>
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<li>LinearRange: models lb <= sum_{i in S} a_i*x_i <= ub, and it provides various operator overloads to build up "LinearExpr"s and then convert them to "LinearRange"s.</li>
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</ol>
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<p >Recommended use (avoids dangerous code):</p>
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<div class="fragment"><div class="line">MPSolver solver = ...;</div>
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<div class="line"><span class="keyword">const</span> LinearExpr x = solver.MakeVar(...); * Note: implicit conversion</div>
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<div class="line"><span class="keyword">const</span> LinearExpr y = solver.MakeVar(...);</div>
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<div class="line"><span class="keyword">const</span> LinearExpr z = solver.MakeVar(...);</div>
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<div class="line"><span class="keyword">const</span> LinearExpr e1 = x + y;</div>
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<div class="line"><span class="keyword">const</span> LinearExpr e2 = (e1 + 7.0 + z)/3.0;</div>
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<div class="line"><span class="keyword">const</span> LinearRange r = e1 <= e2;</div>
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<div class="line">solver.MakeRowConstraint(r);</div>
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</div><!-- fragment --><p ><b>WARNING</b>, AVOID THIS TRAP:</p>
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<div class="fragment"><div class="line">MPSolver solver = ...;</div>
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<div class="line">MPVariable* x = solver.MakeVar(...);</div>
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<div class="line">LinearExpr y = x + 5;</div>
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</div><!-- fragment --><p >In evaluating "x+5" above, x is NOT converted to a LinearExpr before the addition, but rather is treated as a pointer, so x+5 gives a new pointer to garbage memory.</p>
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<p >For this reason, when using LinearExpr, it is best practice to:</p><ol type="1">
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<li>use double literals instead of ints (e.g. "x + 5.0", not "x + 5"),</li>
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<li>Immediately convert all MPVariable* to LinearExpr on creation, and only hold references to the "LinearExpr"s.</li>
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</ol>
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<p >Likewise, the following code is NOT recommended: </p><div class="fragment"><div class="line">MPSolver solver = ...;</div>
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<div class="line">MPVariable* x = solver.MakeVar(...);</div>
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<div class="line">MPVariable* y = solver.MakeVar(...);</div>
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<div class="line">LinearExpr e1 = LinearExpr(x) + y + 5;</div>
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</div><!-- fragment --><p >While it is correct, it violates the natural assumption that the + operator is associative. Thus you are setting a trap for future modifications of the code, as any of the following changes would lead to the above failure mode:</p>
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<ul>
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<li><div class="fragment"><div class="line">LinearExpr e1 = LinearExpr(x) + (y + 5); </div>
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</div><!-- fragment --></li>
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<li><div class="fragment"><div class="line">LinearExpr e1 = y + 5 + LinearExpr(x); </div>
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</div><!-- fragment --> </li>
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</ul>
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<p class="definition">Definition in file <a class="el" href="linear__expr_8h_source.html">linear_expr.h</a>.</p>
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</div>
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<p><a href="linear__expr_8h_source.html">Go to the source code of this file.</a></p>
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<table class="memberdecls">
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a id="nested-classes" name="nested-classes"></a>
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Classes</h2></td></tr>
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<tr class="memitem:"><td class="memItemLeft" align="right" valign="top">class  </td><td class="memItemRight" valign="bottom"><a class="el" href="classoperations__research_1_1_linear_expr.html">LinearExpr</a></td></tr>
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<tr class="memdesc:"><td class="mdescLeft"> </td><td class="mdescRight"><a class="el" href="classoperations__research_1_1_linear_expr.html" title="LinearExpr models a quantity that is linear in the decision variables (MPVariable) of an optimization...">LinearExpr</a> models a quantity that is linear in the decision variables (<a class="el" href="classoperations__research_1_1_m_p_variable.html" title="The class for variables of a Mathematical Programming (MP) model.">MPVariable</a>) of an optimization problem, i.e. <a href="classoperations__research_1_1_linear_expr.html#details">More...</a><br /></td></tr>
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<tr class="separator:"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:"><td class="memItemLeft" align="right" valign="top">class  </td><td class="memItemRight" valign="bottom"><a class="el" href="classoperations__research_1_1_linear_range.html">LinearRange</a></td></tr>
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<tr class="memdesc:"><td class="mdescLeft"> </td><td class="mdescRight">An expression of the form: <a href="classoperations__research_1_1_linear_range.html#details">More...</a><br /></td></tr>
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<tr class="separator:"><td class="memSeparator" colspan="2"> </td></tr>
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</table><table class="memberdecls">
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a id="namespaces" name="namespaces"></a>
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Namespaces</h2></td></tr>
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<tr class="memitem:namespaceoperations__research"><td class="memItemLeft" align="right" valign="top">namespace  </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html">operations_research</a></td></tr>
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<tr class="memdesc:namespaceoperations__research"><td class="mdescLeft"> </td><td class="mdescRight">Collection of objects used to extend the <a class="el" href="classoperations__research_1_1_constraint.html" title="A constraint is the main modeling object.">Constraint</a> <a class="el" href="classoperations__research_1_1_solver.html" title="Solver Class.">Solver</a> library. <br /></td></tr>
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<tr class="separator:"><td class="memSeparator" colspan="2"> </td></tr>
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</table><table class="memberdecls">
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a id="func-members" name="func-members"></a>
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Functions</h2></td></tr>
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<tr class="memitem:a4d39af6692e71ee2b0191f0a9d46b764"><td class="memItemLeft" align="right" valign="top">std::ostream & </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#a4d39af6692e71ee2b0191f0a9d46b764">operator<<</a> (std::ostream &stream, const LinearExpr &linear_expr)</td></tr>
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<tr class="separator:a4d39af6692e71ee2b0191f0a9d46b764"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:a118de93231a6290e4f98ce5d981fd903"><td class="memItemLeft" align="right" valign="top">LinearExpr </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#a118de93231a6290e4f98ce5d981fd903">operator+</a> (LinearExpr lhs, const LinearExpr &rhs)</td></tr>
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<tr class="separator:a118de93231a6290e4f98ce5d981fd903"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:a9a57971e3ced4a836ed66de9dc3b657d"><td class="memItemLeft" align="right" valign="top">LinearExpr </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#a9a57971e3ced4a836ed66de9dc3b657d">operator-</a> (LinearExpr lhs, const LinearExpr &rhs)</td></tr>
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<tr class="separator:a9a57971e3ced4a836ed66de9dc3b657d"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:a66066138340286e4386bbb3de7eafdf4"><td class="memItemLeft" align="right" valign="top">LinearExpr </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#a66066138340286e4386bbb3de7eafdf4">operator*</a> (LinearExpr lhs, double rhs)</td></tr>
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<tr class="separator:a66066138340286e4386bbb3de7eafdf4"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:a81b3f73c470d398ce42791b85964e90f"><td class="memItemLeft" align="right" valign="top">LinearExpr </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#a81b3f73c470d398ce42791b85964e90f">operator/</a> (LinearExpr lhs, double rhs)</td></tr>
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<tr class="separator:a81b3f73c470d398ce42791b85964e90f"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:a4ad9d128501e5d521839ad16cdc82d39"><td class="memItemLeft" align="right" valign="top">LinearExpr </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#a4ad9d128501e5d521839ad16cdc82d39">operator*</a> (double lhs, LinearExpr rhs)</td></tr>
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<tr class="separator:a4ad9d128501e5d521839ad16cdc82d39"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:ad0e6185e1b4809a4edd6cc31ac00d7e2"><td class="memItemLeft" align="right" valign="top">LinearRange </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#ad0e6185e1b4809a4edd6cc31ac00d7e2">operator<=</a> (const LinearExpr &lhs, const LinearExpr &rhs)</td></tr>
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<tr class="separator:ad0e6185e1b4809a4edd6cc31ac00d7e2"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:ae161405d349af5d521fa0fd25c3b6f83"><td class="memItemLeft" align="right" valign="top">LinearRange </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#ae161405d349af5d521fa0fd25c3b6f83">operator==</a> (const LinearExpr &lhs, const LinearExpr &rhs)</td></tr>
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<tr class="separator:ae161405d349af5d521fa0fd25c3b6f83"><td class="memSeparator" colspan="2"> </td></tr>
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<tr class="memitem:ab7cf6c0298d3fa64034fe8d1eff683f6"><td class="memItemLeft" align="right" valign="top">LinearRange </td><td class="memItemRight" valign="bottom"><a class="el" href="namespaceoperations__research.html#ab7cf6c0298d3fa64034fe8d1eff683f6">operator>=</a> (const LinearExpr &lhs, const LinearExpr &rhs)</td></tr>
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