1 | // ideal_stuff.cc |
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2 | |
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3 | // implementation of the special ideal features needed by the IP-algorithms |
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4 | |
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5 | #ifndef IDEAL_STUFF_CC |
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6 | #define IDEAL_STUFF_CC |
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7 | |
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8 | #include "ideal.h" |
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9 | |
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10 | ////////////////////// elimination stuff /////////////////////////////////// |
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11 | |
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12 | ideal& ideal::eliminate() |
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13 | { |
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14 | // eliminates the generators of the ideal involving elimination variables |
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15 | // with respect to w |
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16 | |
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17 | if(w.number_of_elimination_variables()<=0) |
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18 | // elimination unnecessary |
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19 | return *this; |
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20 | |
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21 | list_iterator iter; |
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22 | |
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23 | #ifdef NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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24 | |
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25 | // Simply iterate over the generator list and delete the elements involving |
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26 | // elimination variables. |
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27 | // There is no need to change the done/undone or the reduced/unreduced mark of |
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28 | // an element. |
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29 | |
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30 | iter.set_to_list(generators); |
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31 | |
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32 | while((iter.is_at_end())==FALSE) |
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33 | { |
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34 | binomial& bin=iter.get_element(); |
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35 | |
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36 | if(bin.involves_elimination_variables(w)==TRUE) |
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37 | { |
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38 | iter.delete_element(); |
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39 | size--; |
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40 | } |
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41 | else |
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42 | { |
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43 | bin.drop_elimination_variables(w); |
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44 | iter.next(); |
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45 | } |
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46 | } |
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47 | |
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48 | #endif // NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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49 | |
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50 | |
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51 | #ifdef SUPPORT_DRIVEN_METHODS_EXTENDED |
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52 | |
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53 | // Iterate over the generator lists and check whether the elements involve |
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54 | // elimination variables. |
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55 | // As the set of support variables can be changed by the elimination, the |
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56 | // elements that are not deleted are first moved to the aux_list and then |
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57 | // reinserted according to their new support. |
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58 | // The elimination variables are droppd while reinserting. |
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59 | // In general, elimination is done only once. The time needed for this is |
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60 | // linear in the number of generators (in the Groebner basis). The elimination |
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61 | // itself is therefore very fast in comparison to the Groebner basis |
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62 | // computation needed for it... So we renounce to a complicated optimization |
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63 | // of this procedure (the support information is not used). In fact, tests |
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64 | // show that elimination time is really negligible. |
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65 | |
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66 | // elimination |
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67 | for(short i=0;i<Number_of_Lists;i++) |
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68 | { |
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69 | iter.set_to_list(generators[i]); |
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70 | |
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71 | while((iter.is_at_end())==FALSE) |
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72 | { |
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73 | binomial& bin=iter.get_element(); |
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74 | |
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75 | if(bin.involves_elimination_variables(w)==TRUE) |
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76 | { |
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77 | iter.delete_element(); |
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78 | size--; |
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79 | } |
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80 | else |
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81 | { |
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82 | aux_list._insert(bin); |
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83 | iter.extract_element(); |
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84 | // As the generators are reinserted later, we do not decrement the |
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85 | // size (and so do not need to increment it during reinsertion). |
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86 | } |
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87 | } |
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88 | } |
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89 | |
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90 | // reinsertion |
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91 | iter.set_to_list(aux_list); |
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92 | |
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93 | while(iter.is_at_end()==FALSE) |
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94 | { |
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95 | binomial& bin=iter.get_element(); |
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96 | bin.drop_elimination_variables(w); |
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97 | generators[bin.head_support%Number_of_Lists].insert(bin); |
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98 | // size is not incremented, see above... |
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99 | iter.extract_element(); |
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100 | } |
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101 | |
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102 | #endif // SUPPORT_DRIVEN_METHODS_EXTENDED |
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103 | |
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104 | |
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105 | // finally adapt term ordering |
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106 | w.convert_to_weighted_ordering(); |
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107 | |
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108 | return *this; |
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109 | } |
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110 | |
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111 | |
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112 | |
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113 | |
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114 | ideal& ideal::pseudo_eliminate() |
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115 | { |
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116 | |
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117 | if(w.number_of_weighted_variables()<=0) |
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118 | { |
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119 | cerr<<"WARNING: ideal& ideal::pseudo_eliminate():\n" |
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120 | "cannot be performed without weighted variables"<<endl; |
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121 | return *this; |
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122 | } |
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123 | |
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124 | |
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125 | list_iterator iter; |
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126 | |
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127 | short last_weighted_variable=w.number_of_weighted_variables()-1; |
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128 | |
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129 | |
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130 | #ifdef NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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131 | |
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132 | // Simply iterate over the generator list and delete the elements involving |
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133 | // the last weighted variable. |
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134 | // There is no need to change the done/undone or the reduced/unreduced mark of |
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135 | // an element. |
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136 | |
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137 | iter.set_to_list(generators); |
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138 | |
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139 | while(iter.is_at_end()==FALSE) |
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140 | { |
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141 | binomial& bin=iter.get_element(); |
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142 | |
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143 | if(bin[last_weighted_variable]!=0) |
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144 | // weighted variable to drop is involved in bin |
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145 | { |
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146 | iter.delete_element(); |
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147 | size--; |
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148 | } |
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149 | else |
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150 | { |
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151 | bin.drop_last_weighted_variable(w); |
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152 | iter.next(); |
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153 | } |
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154 | } |
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155 | |
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156 | #endif // NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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157 | |
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158 | |
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159 | #ifdef SUPPORT_DRIVEN_METHODS_EXTENDED |
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160 | |
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161 | // Iterate over the generator lists and check whether the elements involve |
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162 | // the last weighted variable. |
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163 | // As the set of support variables can be changed by the pseudo-elimination, |
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164 | // the elements that are not deleted are first moved to the aux_list and then |
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165 | // reinserted according to their new support. |
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166 | // The last weight variable is dropped while reinserting. |
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167 | // For the time needed by this function see the remarks for ideal::eliminate(). |
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168 | |
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169 | for(short i=0;i<Number_of_Lists;i++) |
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170 | { |
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171 | iter.set_to_list(generators[i]); |
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172 | |
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173 | while((iter.is_at_end())==FALSE) |
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174 | { |
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175 | binomial& bin=iter.get_element(); |
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176 | |
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177 | if(bin[last_weighted_variable]!=0) |
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178 | { |
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179 | iter.delete_element(); |
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180 | size--; |
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181 | } |
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182 | else |
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183 | { |
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184 | aux_list._insert(bin); |
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185 | iter.extract_element(); |
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186 | // As the generators are reinserted later, we do not decrement the |
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187 | // size (and so do not need to increment it during reinsertion). |
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188 | } |
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189 | } |
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190 | } |
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191 | |
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192 | |
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193 | iter.set_to_list(aux_list); |
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194 | |
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195 | while(iter.is_at_end()==FALSE) |
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196 | { |
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197 | binomial& bin=iter.get_element(); |
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198 | bin.drop_last_weighted_variable(w); |
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199 | generators[bin.head_support%Number_of_Lists].insert(bin); |
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200 | // size is not incremented, see above... |
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201 | iter.extract_element(); |
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202 | } |
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203 | |
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204 | #endif // SUPPORT_DRIVEN_METHODS_EXTENDED |
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205 | |
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206 | // finally adapt term ordering |
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207 | w.delete_last_weighted_variable(); |
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208 | |
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209 | return *this; |
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210 | } |
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211 | |
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212 | |
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213 | |
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214 | |
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215 | /////////////////// management of the term ordering ///////////////////////// |
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216 | |
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217 | |
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218 | |
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219 | |
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220 | ideal& ideal::change_term_ordering_to(const term_ordering& _w) |
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221 | { |
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222 | |
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223 | // first check compatibility |
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224 | if((w.number_of_weighted_variables()+w.number_of_elimination_variables())!= |
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225 | (_w.number_of_weighted_variables()+_w.number_of_elimination_variables())) |
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226 | { |
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227 | cerr<<"WARNING: ideal& ideal::change_term_ordering_to" |
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228 | "(const term_ordering&):\nincompatibility detected, term ordering not" |
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229 | "changed."<<endl; |
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230 | return *this; |
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231 | } |
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232 | |
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233 | // change term ordering |
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234 | w=_w; |
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235 | |
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236 | list_iterator iter; |
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237 | |
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238 | |
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239 | #ifdef NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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240 | |
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241 | // Simply iterate over the generator list. Because the change of the term |
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242 | // ordering, the "done" and "reduced" marks of the elements have to be deleted. |
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243 | |
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244 | iter.set_to_list(generators); |
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245 | |
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246 | while((iter.is_at_end())==FALSE) |
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247 | { |
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248 | (iter.get_element()).adapt_to_term_ordering(w); |
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249 | iter.mark_element_undone(); |
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250 | iter.mark_element_head_unreduced(); |
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251 | iter.next(); |
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252 | } |
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253 | |
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254 | #endif // NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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255 | |
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256 | |
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257 | #ifdef SUPPORT_DRIVEN_METHODS_EXTENDED |
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258 | |
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259 | // As head and tail might have to be exchanged, the elements are first moved to |
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260 | // the aux_list and then reinserted according to their new head. |
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261 | |
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262 | for(short i=0;i<Number_of_Lists;i++) |
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263 | { |
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264 | iter.set_to_list(generators[i]); |
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265 | |
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266 | while((iter.is_at_end())==FALSE) |
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267 | { |
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268 | binomial& bin=iter.get_element(); |
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269 | |
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270 | if(bin.adapt_to_term_ordering(w)==-1) |
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271 | // head and tail exchanged |
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272 | { |
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273 | aux_list._insert(bin); |
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274 | iter.extract_element(); |
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275 | // As the generators are reinserted later, we do not decrement the |
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276 | // size (and so do not need to increment it during reinsertion). |
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277 | } |
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278 | else |
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279 | { |
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280 | // Although the S-pairs of the remaining elements have already been |
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281 | // computed once, the "done" marks have to be deleted: With a new |
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282 | // term ordering, the results of the S-pair reduction can change - |
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283 | // as well as the interreduction results. |
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284 | iter.mark_element_undone(); |
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285 | iter.mark_element_head_unreduced(); |
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286 | iter.next(); |
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287 | } |
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288 | } |
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289 | } |
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290 | |
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291 | // reinsertion |
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292 | iter.set_to_list(aux_list); |
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293 | |
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294 | while(iter.is_at_end()==FALSE) |
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295 | { |
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296 | binomial& bin=iter.get_element(); |
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297 | generators[bin.head_support%Number_of_Lists].insert(bin); |
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298 | // size is not incremented, see above... |
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299 | iter.extract_element(); |
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300 | } |
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301 | |
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302 | #endif // SUPPORT_DRIVEN_METHODS_EXTENDED |
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303 | |
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304 | |
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305 | return *this; |
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306 | } |
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307 | |
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308 | |
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309 | |
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310 | |
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311 | /////////// manipulation of the variables /////////////////////////////////// |
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312 | |
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313 | |
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314 | |
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315 | |
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316 | ideal& ideal::swap_variables_unsafe(const short& i, const short& j) |
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317 | { |
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318 | // first check arguments |
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319 | if((i<0) || (i>=w.number_of_weighted_variables()) |
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320 | || (j<0) || (j>=w.number_of_weighted_variables())) |
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321 | { |
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322 | cout<<"WARNING: ideal::swap_variables(const short&, const short&)\n " |
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323 | "or ideal::swap_variables_unsafe(const short&, const short&):\n" |
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324 | "index out of range"<<endl; |
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325 | return *this; |
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326 | } |
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327 | |
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328 | if(i==j) |
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329 | return(*this); |
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330 | // special case to avoid unnecessary overhead |
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331 | |
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332 | |
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333 | list_iterator iter; |
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334 | |
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335 | |
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336 | #ifdef NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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337 | |
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338 | iter.set_to_list(generators); |
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339 | |
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340 | while((iter.is_at_end())==FALSE) |
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341 | { |
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342 | (iter.get_element()).swap_variables(i,j); |
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343 | iter.next(); |
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344 | } |
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345 | |
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346 | #endif // NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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347 | |
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348 | |
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349 | #ifdef SUPPORT_DRIVEN_METHODS_EXTENDED |
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350 | |
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351 | // As head_support and tail_support are manipulated, the elements are first |
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352 | // moved to the aux_list and then reinserted according to their new head. |
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353 | // But head and tail are not adapted to the new term ordering induced by |
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354 | // the change of the variable order - this is only done in the "safe" |
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355 | // routine swap_variables(const short&, const short&). |
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356 | |
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357 | for(short l=0;l<Number_of_Lists;l++) |
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358 | { |
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359 | iter.set_to_list(generators[l]); |
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360 | |
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361 | while((iter.is_at_end())==FALSE) |
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362 | { |
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363 | binomial& bin=iter.get_element(); |
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364 | bin.swap_variables(i,j); |
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365 | aux_list._insert(bin); |
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366 | iter.extract_element(); |
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367 | // As the generators are reinserted later, we do not decrement the |
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368 | // size (and so do not need to increment it during reinsertion). |
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369 | } |
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370 | } |
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371 | |
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372 | // reinsertion |
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373 | iter.set_to_list(aux_list); |
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374 | |
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375 | while(iter.is_at_end()==FALSE) |
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376 | { |
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377 | binomial& bin=iter.get_element(); |
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378 | generators[bin.head_support%Number_of_Lists].insert(bin); |
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379 | // size is not incremented, see above... |
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380 | iter.extract_element(); |
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381 | } |
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382 | |
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383 | #endif // SUPPORT_DRIVEN_METHODS_EXTENDED |
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384 | |
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385 | |
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386 | // finally adapt term ordering |
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387 | w.swap_weights(i,j); |
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388 | |
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389 | return *this; |
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390 | } |
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391 | |
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392 | |
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393 | |
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394 | |
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395 | ideal& ideal::swap_variables(const short& i, const short& j) |
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396 | { |
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397 | |
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398 | swap_variables_unsafe(i,j); |
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399 | |
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400 | change_term_ordering_to(w); |
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401 | // This rebuilds the list structure... |
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402 | |
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403 | return *this; |
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404 | } |
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405 | |
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406 | |
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407 | |
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408 | |
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409 | ideal& ideal::flip_variable_unsafe(const short& i) |
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410 | { |
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411 | // first check argument |
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412 | if((i<0) || (i>=w.number_of_weighted_variables())) |
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413 | { |
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414 | cout<<"WARNING: ideal::flip_variables(const short&):\n" |
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415 | "argument out of range, nothing done"<<endl; |
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416 | return *this; |
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417 | } |
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418 | |
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419 | |
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420 | list_iterator iter; |
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421 | |
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422 | |
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423 | #ifdef NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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424 | |
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425 | iter.set_to_list(generators); |
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426 | |
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427 | while((iter.is_at_end())==FALSE) |
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428 | { |
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429 | (iter.get_element()).flip_variable(i); |
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430 | iter.next(); |
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431 | } |
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432 | |
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433 | #endif // NO_SUPPORT_DRIVEN_METHODS_EXTENDED |
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434 | |
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435 | |
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436 | #ifdef SUPPORT_DRIVEN_METHODS_EXTENDED |
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437 | |
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438 | // As head_support and tail_support can change, the elements are first moved |
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439 | // to the aux_list and then reinserted according to their new head. |
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440 | |
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441 | for(short l=0;l<Number_of_Lists;l++) |
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442 | { |
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443 | iter.set_to_list(generators[l]); |
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444 | |
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445 | while((iter.is_at_end())==FALSE) |
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446 | { |
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447 | binomial& bin=iter.get_element(); |
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448 | bin.flip_variable(i); |
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449 | aux_list._insert(bin); |
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450 | iter.extract_element(); |
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451 | // As the generators are reinserted later, we do not decrement the |
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452 | // size (and so do not need to increment it during reinsertion). |
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453 | } |
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454 | } |
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455 | |
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456 | // reinsertion |
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457 | iter.set_to_list(aux_list); |
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458 | |
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459 | while(iter.is_at_end()==FALSE) |
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460 | { |
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461 | binomial& bin=iter.get_element(); |
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462 | generators[bin.head_support%Number_of_Lists].insert(bin); |
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463 | iter.extract_element(); |
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464 | // size is not incremented, see above... |
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465 | } |
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466 | |
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467 | #endif // SUPPORT_DRIVEN_METHODS_EXTENDED |
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468 | |
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469 | return *this; |
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470 | } |
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471 | #endif // IDEAL_STUFF_CC |
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