1 | // $Id: link.cpp 1902 2013-04-10 16:58:16Z stefan $ |
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2 | // Copyright (C) 2005, International Business Machines |
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3 | // Corporation and others. All Rights Reserved. |
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4 | // This code is licensed under the terms of the Eclipse Public License (EPL). |
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5 | |
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6 | #include <cassert> |
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7 | #include <iomanip> |
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8 | |
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9 | #include "CoinPragma.hpp" |
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10 | // For Branch and bound |
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11 | #include "OsiSolverInterface.hpp" |
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12 | #include "CbcModel.hpp" |
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13 | #include "CoinModel.hpp" |
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14 | // For Linked Ordered Sets |
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15 | #include "CbcBranchLink.hpp" |
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16 | #include "OsiClpSolverInterface.hpp" |
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17 | |
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18 | #include "CoinTime.hpp" |
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19 | |
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20 | |
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21 | /************************************************************************ |
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22 | |
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23 | This shows how we can define a new branching method to solve problems with |
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24 | nonlinearities and discontinuities. |
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25 | |
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26 | We are going to solve the problem |
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27 | |
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28 | minimize 10.0*x + y + z - w |
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29 | |
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30 | where x, y are continuous between 1 and 10, z can take the values 0, 0.1, 0.2 up to 1.0 |
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31 | and w can take the values 0 or 1. There is one constraint |
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32 | |
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33 | w <= x*z**2 + y*sqrt(z) |
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34 | |
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35 | One could try to use logarithms to make the problem separable but that is a very |
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36 | weak formulation as we want to branch on z directly. The answer is the concept of linked |
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37 | special ordered sets. The generalization with column generation can be even more powerful |
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38 | but here we are limiting z to discrete values to avoid column generation. |
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39 | |
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40 | The idea is simple: |
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41 | |
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42 | A linear variable is a convex combination of its lower bound and upper bound! |
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43 | If x must lie between 2 and 10 then we can substitute for x as x == 2.0*xl + 10.0*xu where |
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44 | xl + xu == 1.0. At first this looks cumbersome but if we have xl0, xl1, ... xl10 and corresponding |
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45 | xu and yl and yu then we can write: |
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46 | |
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47 | x == sum 2.0*xl[i] + 10.0* xu[i] where sum xl[i] + xu[i] == 1.0 |
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48 | and |
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49 | x*z**2 == 0.02*xl1 + 0.1*xu1 + 0.08*xl2 + 0.4*xu2 .... + 2.0*xl10 + 10.0*xu10 |
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50 | |
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51 | with similar substitutions for y and y*sqrt(z) |
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52 | |
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53 | And now the problem is satisfied if w is 0 or 1 and xl[i], xu[i], yl[i] and yu[i] are only |
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54 | nonzero for one i. |
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55 | |
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56 | So this is just like a special ordered set of type 1 but on four sets simultaneously. |
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57 | Also note that convexity requirements for any non-linear functions are not needed. |
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58 | |
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59 | So we need a new branching method to do that - see CbcBranchLink.?pp |
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60 | |
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61 | We are going to need a CbcBranchLink method to see whether we are satisfied etc and also to |
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62 | create another branching object which knows how to fix variables. We might be able to use an |
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63 | existing method for the latter but let us create two methods CbcLink and |
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64 | CbcLinkBranchingObject. |
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65 | |
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66 | For CbcLink we will need the following methods: |
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67 | Constructot/Destructor |
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68 | infeasibility - returns 0.0 if feasible otherwise some measure of infeasibility |
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69 | feasibleRegion - sets bounds to contain current solution |
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70 | createBranch - creates a CbcLinkBranchingObject |
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71 | |
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72 | For CbcLinkBranchingObject we need: |
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73 | Constructor/Destructor |
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74 | branch - does actual fixing |
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75 | print - optional for debug purposes. |
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76 | |
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77 | The easiest way to do this is to cut and paste from CbcBranchActual to get current |
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78 | SOS stuff and then modify that. |
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79 | |
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80 | ************************************************************************/ |
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81 | |
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82 | int main (int argc, const char *argv[]) |
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83 | { |
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84 | |
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85 | OsiClpSolverInterface solver1; |
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86 | |
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87 | // Create model |
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88 | CoinModel build; |
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89 | // Keep x,y and z for reporting purposes in rows 0,1,2 |
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90 | // Do these |
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91 | double value=1.0; |
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92 | int row=-1; |
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93 | // x |
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94 | row=0; |
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95 | build.addColumn(1,&row,&value,1.0,10.0,10.0); |
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96 | // y |
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97 | row=1; |
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98 | build.addColumn(1,&row,&value,1.0,10.0,1.0); |
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99 | // z |
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100 | row=2; |
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101 | build.addColumn(1,&row,&value,0.0,1.0,1.0); |
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102 | // w |
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103 | row=3; |
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104 | build.addColumn(1,&row,&value,0.0,1.0,-1.0); |
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105 | build.setInteger(3); |
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106 | // Do columns so we know where each is |
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107 | int i; |
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108 | for (i=4;i<4+44;i++) |
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109 | build.setColumnBounds(i,0.0,1.0); |
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110 | // Now do rows |
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111 | // x |
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112 | build.setRowBounds(0,0.0,0.0); |
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113 | for (i=0;i<11;i++) { |
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114 | // xl |
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115 | build.setElement(0,4+4*i,-1.0); |
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116 | // xu |
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117 | build.setElement(0,4+4*i+1,-10.0); |
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118 | } |
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119 | // y |
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120 | build.setRowBounds(1,0.0,0.0); |
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121 | for (i=0;i<11;i++) { |
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122 | // yl |
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123 | build.setElement(1,4+4*i+2,-1.0); |
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124 | // yu |
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125 | build.setElement(1,4+4*i+3,-10.0); |
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126 | } |
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127 | // z - just use x part |
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128 | build.setRowBounds(2,0.0,0.0); |
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129 | for (i=0;i<11;i++) { |
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130 | // xl |
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131 | build.setElement(2,4+4*i,-0.1*i); |
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132 | // xu |
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133 | build.setElement(2,4+4*i+1,-0.1*i); |
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134 | } |
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135 | // w <= x*z**2 + y* sqrt(z) |
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136 | build.setRowBounds(3,-COIN_DBL_MAX,0.0); |
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137 | for (i=0;i<11;i++) { |
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138 | double value = 0.1*i; |
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139 | // xl * z**2 |
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140 | build.setElement(3,4+4*i,-1.0*value*value); |
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141 | // xu * z**2 |
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142 | build.setElement(3,4+4*i+1,-10.0*value*value); |
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143 | // yl * sqrt(z) |
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144 | build.setElement(3,4+4*i+2,-1.0*sqrt(value)); |
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145 | // yu * sqrt(z) |
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146 | build.setElement(3,4+4*i+3,-10.0*sqrt(value)); |
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147 | } |
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148 | // and convexity for x and y |
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149 | // x |
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150 | build.setRowBounds(4,1.0,1.0); |
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151 | for (i=0;i<11;i++) { |
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152 | // xl |
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153 | build.setElement(4,4+4*i,1.0); |
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154 | // xu |
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155 | build.setElement(4,4+4*i+1,1.0); |
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156 | } |
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157 | // y |
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158 | build.setRowBounds(5,1.0,1.0); |
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159 | for (i=0;i<11;i++) { |
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160 | // yl |
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161 | build.setElement(5,4+4*i+2,1.0); |
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162 | // yu |
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163 | build.setElement(5,4+4*i+3,1.0); |
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164 | } |
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165 | solver1.loadFromCoinModel(build); |
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166 | // To make CbcBranchLink simpler assume that all variables with same i are consecutive |
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167 | |
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168 | double time1 = CoinCpuTime(); |
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169 | solver1.initialSolve(); |
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170 | solver1.writeMps("bad"); |
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171 | CbcModel model(solver1); |
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172 | model.solver()->setHintParam(OsiDoReducePrint,true,OsiHintTry); |
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173 | // Although just one set - code as if more |
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174 | CbcObject ** objects = new CbcObject * [1]; |
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175 | /* Format is number in sets, number in each link, first variable in matrix) |
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176 | and then a weight for each in set to say where to branch. |
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177 | Finally a set number as ID. |
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178 | */ |
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179 | double where[]={0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0}; |
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180 | objects[0]=new CbcLink(&model,11,4,4,where,0); |
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181 | model.addObjects(1,objects); |
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182 | delete objects[0]; |
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183 | delete [] objects; |
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184 | // Do complete search |
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185 | |
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186 | model.branchAndBound(); |
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187 | |
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188 | std::cout<<"took "<<CoinCpuTime()-time1<<" seconds, " |
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189 | <<model.getNodeCount()<<" nodes with objective " |
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190 | <<model.getObjValue() |
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191 | <<(!model.status() ? " Finished" : " Not finished") |
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192 | <<std::endl; |
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193 | |
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194 | |
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195 | if (model.getMinimizationObjValue()<1.0e50) { |
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196 | |
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197 | const double * solution = model.bestSolution(); |
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198 | // check correct |
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199 | int which=-1; |
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200 | for (int i=0;i<11;i++) { |
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201 | for (int j=4+4*i;j<4+4*i+4;j++) { |
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202 | double value=solution[j]; |
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203 | if (fabs(value)>1.0e-7) { |
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204 | if (which==-1) |
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205 | which=i; |
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206 | else |
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207 | assert (which==i); |
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208 | } |
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209 | } |
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210 | } |
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211 | double x=solution[0]; |
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212 | double y=solution[1]; |
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213 | double z=solution[2]; |
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214 | double w=solution[3]; |
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215 | // check z |
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216 | assert (fabs(z-0.1*((double) which))<1.0e-7); |
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217 | printf("Optimal solution when x is %g, y %g, z %g and w %g\n", |
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218 | x,y,z,w); |
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219 | printf("solution should be %g\n",10.0*x+y+z-w); |
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220 | } |
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221 | return 0; |
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222 | } |
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