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| 2 | Simplex-specific Methods |
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| 4 | Basic Model Classes |
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| 8 | Simplex-specific Methods |
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| 9 | </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s06.html">Prev</a> </td><th width="60%" align="center">Chapter 2. |
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| 10 | Basic Model Classes |
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| 11 | </th><td width="20%" align="right"> <a accesskey="n" href="ch02s08.html">Next</a></td></tr></table><hr></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="simplexspecific"></a> |
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| 12 | Simplex-specific Methods |
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| 13 | </h2></div></div></div><p> |
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| 14 | Some of the most commonly-used methods when working with Simplex are listed in |
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| 15 | the table below. |
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| 16 | </p><div class="table"><a name="id4769539"></a><p class="title"><b>Table 2.3. Common Simplex-specific methods</b></p><table summary="Common Simplex-specific methods" border="0"><colgroup><col><col></colgroup><thead><tr><th> |
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| 17 | Method(s) |
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| 18 | </th><th> |
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| 19 | Description |
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| 20 | </th></tr></thead><tbody><tr><td align="left" valign="top"> |
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| 21 | <tt class="function">primal(int mode=0)</tt> |
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| 22 | </td><td align="left" valign="top"> |
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| 23 | This applies the primal algorithm. If <i class="parameter"><tt>mode</tt></i> is |
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| 24 | set to the default of 0, then the method uses the status variables to |
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| 25 | determine basis and solution. If <i class="parameter"><tt>mode</tt></i> is 1 then |
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| 26 | the method does a values pass so variables not in basis are given their |
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| 27 | current values and one pass of variables is done to clean up the basis |
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| 28 | with an equal or better objective value. |
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| 29 | </td></tr><tr><td align="left" valign="top"> |
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| 30 | <tt class="function">dual(int mode=0)</tt> |
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| 31 | </td><td align="left" valign="top"> |
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| 32 | This applies the dual algorithm. if <i class="parameter"><tt>mode</tt></i> is set |
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| 33 | to the default of 0, then the method uses the status variables to |
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| 34 | determine basis and solution. If <i class="parameter"><tt>mode</tt></i> is 1 then |
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| 35 | the method uses input duals and does a values pass so one pass of basic |
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| 36 | variables is done to clean up the duals with an equal or better objective |
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| 37 | value. |
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| 38 | </td></tr><tr><td align="left" valign="top"> |
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| 39 | <tt class="function">scaling(int mode=1)</tt> |
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| 40 | </td><td align="left" valign="top"> |
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| 41 | This method toggles scaling on (<i class="parameter"><tt>mode</tt></i> set to 1) |
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| 42 | and off (<i class="parameter"><tt>mode</tt></i> set to 0). |
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| 43 | </td></tr><tr><td align="left" valign="top"> |
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| 44 | <tt class="function">int crash(double gap,int mode)</tt> |
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| 45 | </td><td align="left" valign="top"> |
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| 46 | This method attemps to improve on an all slack basis. |
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| 47 | For dual this will move variables to the dual feasible bound |
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| 48 | if the gap between bounds is less than <i class="parameter"><tt>gap</tt></i>. Setting |
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| 49 | <i class="parameter"><tt>mode</tt></i> to 0 guesses which algorithm is better, while |
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| 50 | a value of 1 or 2 will result in more work being done. The return code is |
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| 51 | 0 if the basis was not slacks in first case, it is negative if dual is |
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| 52 | preferred or positive if primal. ±1 means an all slack basis seemed |
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| 53 | best, while ±2 means some work was done. |
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| 54 | </td></tr><tr><td align="left" valign="top"> |
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| 55 | <tt class="function">perturb(int mode)</tt> |
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| 56 | </td><td align="left" valign="top"> |
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| 57 | This method toggles perturbation on (<i class="parameter"><tt>mode</tt></i> set to 1) |
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| 58 | and off (<i class="parameter"><tt>mode</tt></i> set to 0). It should be considered |
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| 59 | a work in progress, although on some problems it gives very good results. |
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| 60 | </td></tr><tr><td align="left" valign="top"> |
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| 61 | <tt class="function">factorizationFrequency()</tt><br> |
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| 62 | <tt class="function">setFactorizationFrequency(int value)</tt> |
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| 63 | </td><td align="left" valign="top"> |
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| 64 | These are "get" and "set" methods for the basis matrix |
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| 65 | factorization frequency. The default is to refactor every 200 iterations, |
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| 66 | but it may make more sense to use something such as 100 + the number of |
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| 67 | rows divided by 50. |
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| 68 | </td></tr><tr><td align="left" valign="top"> |
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| 69 | <tt class="function">dualBound()</tt><br> |
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| 70 | <tt class="function">setDualBound(double value)</tt> |
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| 71 | </td><td align="left" valign="top"> |
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| 72 | These are "get" and "set" methods for the |
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| 73 | "dual bound". The CLP dual algorithm declares all problems |
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| 74 | to be dual feasible by putting non-basic variables to correct bounds for |
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| 75 | the reduced cost. If the gap between the bounds is too big then it |
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| 76 | pretends the gap is only the value specified by this set method. |
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| 77 | In essence, this gives a composite dual rather than a pure |
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| 78 | Phase I- Phase II method. |
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| 79 | </td></tr><tr><td align="left" valign="top"> |
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| 80 | <tt class="function">infeasibilityCost()</tt><br> |
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| 81 | <tt class="function">setInfeasibilityCost(double value)</tt> |
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| 82 | </td><td align="left" valign="top"> |
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| 83 | These are the primal analogs to the "dual bound" methods. |
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| 84 | </td></tr><tr><td align="left" valign="top"> |
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| 85 | <tt class="function">numberPrimalInfeasibilities()</tt><br> |
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| 86 | <tt class="function">sumPrimalInfeasibilities()</tt> |
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| 87 | </td><td align="left" valign="top"> |
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| 88 | After a solve, there may be infeasibilities. These methods serve to |
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| 89 | check for said infeasibilities. One could check the solution explicitly |
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| 90 | as well. For a code fragement illustrating this, see |
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| 91 | <a href="ch02s08.html#presolveexample" title="Example 2.3. Presolve code fragment">Example 2.3, “Presolve code fragment”</a>. |
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| 92 | </td></tr></tbody></table></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s06.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch02s08.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Some Useful Set and Get Methods </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> |
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| 93 | Presolve |
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