1 | ======================= |
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2 | coopr.pyomo CHANGELOG |
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3 | ======================= |
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4 | |
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5 | ------------------------------------------------------------------------------- |
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6 | 2.1 |
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7 | ------------------------------------------------------------------------------- |
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8 | |
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9 | - Removed some TBD notes in the Benders example, and checked in the full |
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10 | benders script (a debug version was committed initially, that only |
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11 | dealt with iteration 1). This version replicates, to within precision, |
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12 | the AMPL execution. Should terminate in 5 master iterations. |
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13 | |
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14 | - Misc rework of variable presolving. Now, model statistics are |
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15 | stored in a more obvious location, and using more verbose names. |
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16 | |
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17 | - Added functions that can (1) extract a canonical representation |
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18 | from an expressions, and (2) generate an expression from a canonical |
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19 | representation. |
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20 | |
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21 | - Adding ability to load a list or tuple of values into a Pyomo |
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22 | model. These are loaded into the variables in the order in which the |
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23 | variables are identified. |
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24 | |
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25 | - Updated variable naming. Special symbols are mapped to |
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26 | a name that contains _Q#_, where # the ASCII decimal representation |
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27 | for that symbol. |
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28 | |
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29 | - Added support for denoting constraint inequalities as 'strict'. Added |
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30 | tests to verify that strict inequalities are recognized. |
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31 | |
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32 | - Resolved #3970. When a parameter is specified with a default |
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33 | value, we should be able to refer to its index set directly, since |
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34 | all values are tacitly defined. |
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35 | |
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36 | - Added a 'random' solver for the p-median example. |
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37 | |
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38 | - Added ".solver-mipgap" option to the pyomo script, mirroring recent useful |
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39 | updates to the PH script. |
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40 | |
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41 | - Simplified the syntax for adding a constraint to a Constraint object. |
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42 | |
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43 | - Reworking how components interact with models. Now, components can |
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44 | only be initialized using data from the model that they are associated |
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45 | with. Thus, models and components are tightly coupled. This allows |
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46 | the following syntax: |
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47 | |
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48 | model.x = Param(model.A) |
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49 | model.construct() |
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50 | |
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51 | The construction process uses the model data that is associated with |
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52 | the parameter. Also, this commmit allows models to be components of |
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53 | another model: |
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54 | |
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55 | m1=Model() |
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56 | m2=Model() |
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57 | m2.m1 = m1 |
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58 | |
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59 | Note, however, that model construct is required to be done |
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60 | separately. When model m2 is constructed, the m1 component is not |
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61 | constructed. |
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62 | |
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63 | - Added check to avoid printing an objective with an empty linear sum. |
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64 | |
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65 | - Rework of the amplbook2 examples, and other Pyomo examples. |
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66 | |
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67 | - A change in semantics for setting up dimen and dim. This change requires |
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68 | that users specify dimen in situtations where it is not obvious from the |
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69 | component declaration. For example, if you initialize from a function, |
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70 | then you'll need to specify dimen if the function returns n-tuples. |
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71 | |
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72 | - Added an extension point for plugins that suport model transformations. |
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73 | Two transformations have been defined: a transformation for eliminating |
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74 | fixed variables, and a transformation for relaxing integrality. These |
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75 | can be generically accessed with the apply_transformation() function. |
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76 | |
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77 | - Extended API of the PyomoModel class to add a variety of helper |
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78 | functions (e.g. accessing constraints, variables and objectives). |
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79 | Adding a method for getting the model solution, as a vector. |
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80 | |
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81 | - Added tests to exercise the Pyomo command-line. |
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82 | |
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83 | - Updates to Pyomo command-line options: |
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84 | |
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85 | Added --model-name option, which allows the specification of an object |
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86 | other than 'model' for the model that is optimized. |
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87 | |
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88 | Added support for create_model(), which accepts a dictionary or |
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89 | pyutilib.misc.Container object containing the options specified with the |
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90 | --model-options option. This function returns a model that is optimized. |
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91 | |
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92 | Added the 'errors' debugging mode. When specified, exceptions dump |
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93 | a traceback. Otherwise, exceptions are caught and only the exception |
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94 | string is printed. |
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95 | |
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96 | - Adding support for component index deactivation. This supports the |
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97 | following semantics: |
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98 | |
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99 | model.C = Constraint(model.A) |
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100 | model.C[index].deactivate() |
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101 | |
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102 | Note that the current implementation requires the user to query whether |
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103 | each index is active: |
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104 | |
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105 | if model.C[index].active: |
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106 | # Do something |
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107 | |
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108 | I could have alternatively changed the iterator for the constraint, |
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109 | but then that could mask the existence of a constraint, making it |
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110 | difficult to reactivate. |
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111 | |
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112 | Finally, note that this activation mechanism is independent |
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113 | of the component level activation/deactivation: |
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114 | |
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115 | model.C.deactivate() |
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116 | # All C constraints are deactivated |
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117 | model.C[index].deactivate |
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118 | # You can still manipulate the C constraint |
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119 | model.C.activate() |
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120 | # Now, the C constraint is active, except for the ' |
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121 | # 'index' constraint |
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122 | |
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123 | - A rework of component management in Pyomo. Component types are now |
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124 | managed with the natural class types (e.g. Var for variables, rather |
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125 | than _VarBase). Further, the components should now be accessed with |
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126 | model methods: components() or active_components(). For example, |
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127 | |
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128 | model.components(Var) |
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129 | |
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130 | returns a dictionary of the Var components. |
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131 | |
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132 | - Created the ComponentBase class, which manages the initialization of |
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133 | components. This consolidates the mechanism needed to generalize |
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134 | the component indexing operations. |
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135 | |
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136 | - Reworking SetArray constructor to create temporary set objects for non-set |
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137 | index arguments. These arguments are passed into a Set object |
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138 | with the 'initialize' argument. |
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139 | |
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140 | - Extended the constraint generation logic to evaluate whether the |
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141 | constraint expression contains constant values. This extension allows |
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142 | the following types of constraints to be specified: |
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143 | |
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144 | def f(model) |
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145 | return 0 < model.x |
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146 | |
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147 | def g(model) |
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148 | return model.x == model.y |
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149 | |
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150 | def h(model) |
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151 | return model.y > model.z |
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152 | |
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153 | However, it's pretty clear now that the following cannot be supported in |
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154 | Python: |
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155 | |
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156 | def j(model) |
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157 | return 0 < model.x < 1 |
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158 | |
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159 | To add upper and lower bounds, a user will need to return a tuple value: |
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160 | |
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161 | def j(model) |
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162 | return (0, model.x, 1) |
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163 | |
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164 | or return an expression that is generated incrementally: |
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165 | |
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166 | def j(model) |
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167 | e = 0 < model.x |
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168 | return e < 1 |
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169 | |
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170 | - Significantly changed - and improved - the handling of variable lower |
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171 | and upper bounds. In the old version of pyomo, if parameters were |
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172 | supplied as bounds, the lb/ub were silently ignored when writing |
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173 | LP/NL/etc files. |
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174 | |
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175 | In the new version of pyomo, these parameters are stored and handled |
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176 | to avoid this issue. In particular, the "lb" and "ub" attributes |
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177 | of a variable are either (1) None, (2) a NumericConstant?, or (3) a |
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178 | _ParamBase. The latter two objects share the common () operator. Thus, |
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179 | to access the lb and ub attributes of a variable, one should either |
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180 | test for None, or use lb() or ub() to extract the value. |
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181 | |
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182 | - Added constraint symbol maps when writing NL files, so the constraint names |
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183 | can be mapped back (e.g., when dealing with dual variables in SOL files) |
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184 | into the user-recognized names. |
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185 | |
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186 | ------------------------------------------------------------------------------- |
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187 | 2.0 |
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188 | ------------------------------------------------------------------------------- |
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189 | |
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190 | - Initial release of Coopr to create the coopr.pyomo package. |
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191 | |
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192 | - See coopr.dist for previous ChangeLog information related to Coopr. |
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193 | |
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