1 | /////////////////////////////////////////////////////////////////////////////// |
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2 | version="version divisors.lib 4.2.0.1 Jan_2021 "; // $Id$ |
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3 | category = "Commutative Algebra"; |
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4 | info=" |
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5 | LIBRARY: divisors.lib Divisors and P-Divisors |
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6 | |
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7 | AUTHORS: Janko Boehm boehm@mathematik.uni-kl.de |
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8 | @* Lars Kastner kastner@math.fu-berlin.de |
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9 | @* Benjamin Lorenz blorenz@math.uni-frankfurt.de |
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10 | @* Hans Schoenemann hannes@mathematik.uni-kl.de |
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11 | @* Yue Ren ren@mathematik.uni-kl.de |
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12 | |
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13 | OVERVIEW: |
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14 | |
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15 | We implement a class divisor on an algebraic variety and methods |
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16 | for computing with them. Divisors are represented by tuples of ideals |
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17 | defining the positive and the negative part. In particular, we implement the group |
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18 | structure on divisors, computing global sections and testing linear |
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19 | equivalence. |
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20 | |
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21 | In addition to this we provide a class formaldivisor which implements |
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22 | integer formal sums of divisors (not necessarily prime). A formal divisor |
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23 | can be evaluated to a divisor, and a divisor can be decomposed into |
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24 | a formal sum. |
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25 | |
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26 | Finally we provide a class pdivisor which implements polyhedral formal sums of |
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27 | divisors (P-divisors) where the coefficients are assumed to be polyhedra with fixed tail cone. |
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28 | There is a function to evaluate a P-divisor on a vector in the dual of the tail cone. The |
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29 | result will be a formal divisor. |
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30 | |
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31 | |
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32 | REFERENCES: |
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33 | |
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34 | For the class divisor we closely follow Macaulay2's tutorial on divisors. |
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35 | |
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36 | |
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37 | PROCEDURES: |
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38 | |
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39 | makeDivisor(ideal,ideal) create a divisor |
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40 | divisorplus(divisor,divisor) add two divisors |
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41 | multdivisor(int,divisor) multiply a divisor by an integer |
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42 | negativedivisor(divisor) compute the negative of the divisor |
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43 | normalForm(divisor) normal form of a divisor |
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44 | isEqualDivisor(divisor,divisor) test whether two divisors are equal |
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45 | globalSections(divisor) compute the global sections of a divisor |
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46 | degreeDivisor(divisor) degree of a divisor |
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47 | linearlyEquivalent(divisor,divisor) test whether two divisors a linearly equivalent |
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48 | effective(divisor) compute an effective divisor |
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49 | linearly equivalent to a divisor |
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50 | |
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51 | makeFormalDivisor(list) make a formal integer sum of divisors |
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52 | evaluateFormalDivisor(formaldivisor) evaluate a formal sum of divisors to a divisor |
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53 | formaldivisorplus(formaldivisor,formaldivisor) add two formal divisors |
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54 | negativeformaldivisor(formaldivisor) compute the negative of the formal divisor |
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55 | multformaldivisor(int,formaldivisor) multiply a formal divisor by an integer |
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56 | degreeFormalDivisor(formaldivisor) degree of a formal divisor |
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57 | |
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58 | makePDivisor(List) make a formal polyhedral sum of divisors |
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59 | |
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60 | |
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61 | "; |
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62 | |
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63 | |
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64 | //////////////////////////////////////////////////////////////////////////////// |
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65 | |
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66 | LIB "primdec.lib"; |
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67 | |
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68 | static proc mod_init() |
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69 | { |
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70 | LIB"customstd.so"; |
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71 | LIB"gfanlib.so"; |
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72 | newstruct("divisor","ideal den,ideal num"); |
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73 | newstruct("formaldivisor","list summands"); |
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74 | newstruct("pdivisor","list summands, cone tail"); |
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75 | |
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76 | system("install","divisor","print",divisor_print,1); |
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77 | system("install","divisor","+",divisorplus,2); |
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78 | system("install","divisor","*",proxymultdivisor,2); |
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79 | system("install","formaldivisor","print",formaldivisor_print,1); |
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80 | system("install","formaldivisor","+",formaldivisorplus,2); |
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81 | system("install","formaldivisor","*",proxymultformaldivisor,2); |
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82 | } |
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83 | |
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84 | |
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85 | |
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86 | proc divisor_print(divisor D) |
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87 | "USAGE: divisor_print(D); D; D = divisor. @* |
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88 | ASSUME: D is a divisor. |
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89 | RETURN: Will print D. |
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90 | KEYWORDS: divisors |
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91 | EXAMPLE: example divisor_print; shows an example |
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92 | " |
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93 | { |
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94 | "("+string(D.num)+") - ("+string(D.den)+")"; |
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95 | } |
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96 | example |
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97 | { "EXAMPLE:"; |
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98 | ring r=31991,(x,y,z),dp; |
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99 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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100 | qring Q = std(I); |
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101 | divisor P = makeDivisor(ideal(x,z),ideal(1)); |
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102 | P; |
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103 | } |
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104 | |
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105 | |
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106 | proc formaldivisor_print(formaldivisor fD) |
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107 | "USAGE: formaldivisor_print(D); D; D = formaldivisor. @* |
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108 | ASSUME: fD is a formaldivisor. |
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109 | RETURN: Will print fD. |
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110 | KEYWORDS: divisors |
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111 | EXAMPLE: example formaldivisor_print; shows an example |
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112 | " |
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113 | { |
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114 | int i; string s; list L=fD.summands; |
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115 | list cd; int c; divisor d; |
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116 | string linebreak = |
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117 | " |
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118 | "; |
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119 | for (i=1; i<=size(L); i++) |
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120 | { |
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121 | cd=L[i]; c=cd[1]; d=cd[2]; |
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122 | if (i>1 && c>=0) { s = s + "+"; } |
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123 | s = s + string(c)+"*( ("+string(d.num)+") - ("+string(d.den)+") )"; |
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124 | if (i!=size(L)) { s = s + linebreak; } |
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125 | } |
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126 | s; |
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127 | } |
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128 | example |
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129 | { "EXAMPLE:"; |
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130 | ring r=31991,(x,y,z),dp; |
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131 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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132 | qring Q = std(I); |
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133 | divisor P = makeDivisor(ideal(x,z),ideal(1)); |
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134 | P; |
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135 | } |
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136 | |
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137 | |
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138 | //////////////////////////////////////////////////////////////////////////////// |
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139 | // divisors as numerator and denomiator ideals |
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140 | |
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141 | proc makeDivisor(ideal I, ideal J) |
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142 | "USAGE: makeDivisor(I ,J); I = ideal, J = ideal. @* |
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143 | ASSUME: I and J are ideals in a qring Q of a smooth irreducible variety X |
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144 | such that any ideal in Q satisfies the S2 condition. |
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145 | RETURN: a divisor on X |
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146 | THEORY: The procedure will eliminate all components which are not of codimension 1. |
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147 | The S2 condition requires that every proper nonzero principal ideal |
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148 | has pure codimension 1. |
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149 | KEYWORDS: divisors |
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150 | EXAMPLE: example makeDivisor; shows an example |
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151 | " |
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152 | { |
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153 | divisor C; |
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154 | C.num = purify1(I); |
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155 | C.den = purify1(J); |
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156 | return(C); |
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157 | } |
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158 | |
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159 | example |
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160 | { "EXAMPLE:"; |
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161 | ring r=31991,(x,y,z),dp; |
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162 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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163 | qring Q = std(I); |
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164 | divisor P = makeDivisor(ideal(x,z),ideal(1)); |
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165 | } |
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166 | |
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167 | |
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168 | proc divisorplus(divisor A, divisor B) |
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169 | "USAGE: divisorplus(A ,B); A + B; A = divisor, B = divisor. @* |
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170 | ASSUME: A and B are divisors on X. |
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171 | RETURN: a divisor on X |
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172 | THEORY: The procedure will compute the product of the numerator |
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173 | and denominator ideals, respectively. |
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174 | KEYWORDS: divisors |
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175 | EXAMPLE: example divisorplus; shows an example |
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176 | " |
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177 | { |
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178 | return(makeDivisor(interred(A.num*B.num),interred(A.den*B.den))); |
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179 | } |
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180 | example |
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181 | { "EXAMPLE:"; |
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182 | ring r=31991,(x,y,z),dp; |
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183 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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184 | qring Q = std(I); |
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185 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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186 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
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187 | A+B; |
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188 | } |
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189 | |
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190 | |
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191 | proc multdivisor(int n, divisor A) |
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192 | "USAGE: multdivisor(n ,A); A*n; n = integer, A = divisor.@* |
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193 | ASSUME: n is an integer and A is a divisor on X. |
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194 | RETURN: a divisor on X |
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195 | THEORY: The procedure will compute the n-th power of the numerator |
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196 | and denominator ideals, respectively. |
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197 | KEYWORDS: divisors |
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198 | EXAMPLE: example multdivisor; shows an example |
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199 | " |
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200 | { |
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201 | if (n<0) {return(multdivisor(-n,negativedivisor(A)));} |
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202 | return(makeDivisor(interred((A.num)^n),interred((A.den)^n))); |
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203 | } |
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204 | example |
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205 | { "EXAMPLE:"; |
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206 | ring r=31991,(x,y,z),dp; |
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207 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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208 | qring Q = std(I); |
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209 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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210 | A; |
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211 | divisor D = multdivisor(4,A); |
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212 | D; |
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213 | A*4; |
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214 | } |
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215 | |
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216 | |
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217 | /*** |
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218 | * For operator overloading, which needs a procedure which takes a divisor first |
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219 | * and integer second. |
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220 | **/ |
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221 | proc proxymultdivisor(divisor A, int n) |
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222 | { |
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223 | if (n<0) {return(multdivisor(-n,negativedivisor(A)));} |
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224 | return(makeDivisor(interred((A.num)^n),interred((A.den)^n))); |
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225 | } |
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226 | |
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227 | |
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228 | proc negativedivisor(divisor A) |
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229 | "USAGE: negativedivisor(A); A*(-1); A = divisor.@* |
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230 | ASSUME: A is a divisor on X. |
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231 | RETURN: a divisor on X |
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232 | THEORY: The procedure will interchange the numerator and denominator ideals. |
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233 | KEYWORDS: divisors |
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234 | EXAMPLE: example negativedivisor; shows an example |
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235 | " |
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236 | { |
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237 | divisor B; |
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238 | B.num=A.den; |
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239 | B.den=A.num; |
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240 | return(B); |
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241 | } |
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242 | example |
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243 | { "EXAMPLE:"; |
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244 | ring r=31991,(x,y,z),dp; |
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245 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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246 | qring Q = std(I); |
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247 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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248 | A; |
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249 | divisor D = negativedivisor(A); |
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250 | D; |
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251 | } |
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252 | |
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253 | |
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254 | proc normalForm(divisor A) |
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255 | "USAGE: normalForm(A); A = divisor.@* |
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256 | ASSUME: A is a divisor on X. |
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257 | RETURN: different representative of the same divisor on X |
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258 | THEORY: The procedure will cancel common components of numerator and denominator. |
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259 | KEYWORDS: divisors |
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260 | EXAMPLE: example normalForm; shows an example |
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261 | " |
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262 | { |
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263 | divisor B; |
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264 | B.num=quotient(A.num,A.den); |
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265 | B.den=quotient(A.den,A.num); |
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266 | return(B); |
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267 | } |
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268 | example |
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269 | { "EXAMPLE:"; |
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270 | ring r=31991,(x,y,z),dp; |
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271 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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272 | qring Q = std(I); |
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273 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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274 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
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275 | divisor D = (A+B)+multdivisor(-1,B); |
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276 | D; |
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277 | normalForm(D); |
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278 | } |
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279 | |
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280 | |
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281 | |
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282 | |
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283 | static proc isEqualIdeal(ideal A,ideal B){ |
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284 | return((size(NF(A,std(B)))==0) && (size(NF(B,std(A)))==0)); |
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285 | } |
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286 | |
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287 | |
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288 | proc isEqualDivisor(divisor A,divisor B) |
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289 | "USAGE: isEqualDivisor(A,B); A = divisor, B = divisor.@* |
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290 | ASSUME: A and B are divisors on X. |
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291 | RETURN: int 0 or 1, checks equality of A and B. |
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292 | THEORY: The procedure will compute the normal forms of A and B and compare. |
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293 | KEYWORDS: divisors |
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294 | EXAMPLE: example isEqualDivisor; shows an example |
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295 | " |
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296 | { |
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297 | A=normalForm(A); |
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298 | B=normalForm(B); |
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299 | return((isEqualIdeal(A.num,B.num)) && (isEqualIdeal(A.den,B.den))); |
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300 | } |
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301 | example |
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302 | { "EXAMPLE:"; |
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303 | ring r=31991,(x,y,z),dp; |
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304 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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305 | qring Q = std(I); |
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306 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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307 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
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308 | divisor D = (A+B)+multdivisor(-1,B); |
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309 | isEqualDivisor(A,D); |
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310 | } |
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311 | |
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312 | |
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313 | static proc purify1(ideal I) |
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314 | { |
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315 | I = simplify(I,2); |
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316 | if (I[1]==0){ERROR("expected a non-zero ideal");} |
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317 | ideal f = I[1]; |
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318 | return(minbase(quotient(f,quotient(f,I)))); |
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319 | } |
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320 | |
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321 | |
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322 | static proc basis(ideal I,int d) |
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323 | { |
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324 | I=simplify(jet(intersect(I,maxideal(d)),d),2); |
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325 | return(I)} |
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326 | |
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327 | //basis(ideal(x,y^3),2); |
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328 | |
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329 | |
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330 | proc globalSections(divisor D) |
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331 | "USAGE: globalSections(A); A = divisor.@* |
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332 | ASSUME: A is a divisor on X. |
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333 | RETURN: a list with a basis of the space of global sections of D. |
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334 | THEORY: We assume that the qring of X satisfies the S2-condition and that X is smooth. We compute sat((f*J) : I) /f |
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335 | where D = (I)-(J). |
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336 | KEYWORDS: divisors |
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337 | EXAMPLE: example globalSections; shows an example |
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338 | " |
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339 | { |
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340 | poly f =(simplify(D.num,2))[1]; |
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341 | ideal LD = basis(purify1(quotient(f*D.den,D.num)),deg(f)); |
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342 | list L = simplify(LD,2),f; |
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343 | return(L); |
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344 | } |
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345 | example |
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346 | { "EXAMPLE:"; |
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347 | ring r=31991,(x,y,z),dp; |
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348 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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349 | qring Q = std(I); |
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350 | divisor P = makeDivisor(ideal(x,z),ideal(1)); |
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351 | divisor D = multdivisor(4,P); |
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352 | globalSections(D); |
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353 | } |
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354 | |
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355 | |
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356 | static proc sectionIdeal(poly f, poly g, divisor D){ |
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357 | return(purify1(quotient(quotient(f*D.num,g), D.den))); |
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358 | } |
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359 | |
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360 | proc degreeDivisor(divisor A) |
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361 | "USAGE: degreeDivisor(A); A = divisor.@* |
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362 | ASSUME: A is a divisor on X. |
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363 | RETURN: The degree of A. |
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364 | THEORY: We compute difference of the degrees of the numerator and denominator ideals. |
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365 | KEYWORDS: divisors |
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366 | EXAMPLE: example degreeDivisor; shows an example |
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367 | " |
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368 | { |
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369 | return( mult(std(A.num))-mult(std(A.den))); |
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370 | } |
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371 | example |
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372 | { "EXAMPLE:"; |
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373 | ring r=31991,(x,y,z),dp; |
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374 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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375 | qring Q = std(I); |
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376 | divisor P = makeDivisor(ideal(x,z),ideal(1)); |
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377 | degreeDivisor(P); |
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378 | } |
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379 | |
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380 | proc linearlyEquivalent(divisor A, divisor B) |
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381 | "USAGE: linearlyEquivalent(A,B); A = divisor, B = divisor.@* |
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382 | ASSUME: A and B are divisors on X. |
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383 | RETURN: list if A and B a linearly equivalent and int 0 otherwise. |
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384 | THEORY: Checks whether A-B is principle. If yes, returns a list L=(f,g) where |
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385 | A - B = (f/g). |
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386 | KEYWORDS: divisors |
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387 | EXAMPLE: example linearlyEquivalent; shows an example |
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388 | " |
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389 | { |
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390 | divisor F = normalForm(divisorplus(A,negativedivisor(B))); |
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391 | list LB = globalSections(F); |
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392 | if (size(LB[1])!=1) {return(0);} |
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393 | ideal V = sectionIdeal(LB[1][1,1],LB[2],F); |
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394 | if (isEqualIdeal(V,ideal(1))==1) {return(list(LB[1][1,1],LB[2]));} |
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395 | return(0); |
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396 | } |
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397 | example |
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398 | { "EXAMPLE:"; |
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399 | ring r=31991,(x,y,z),dp; |
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400 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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401 | qring Q = std(I); |
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402 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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403 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
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404 | linearlyEquivalent(A,B); |
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405 | linearlyEquivalent(multdivisor(2,A),multdivisor(2,B)); |
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406 | } |
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407 | |
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408 | |
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409 | proc effective(divisor A) |
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410 | "USAGE: effective(A); A = divisor.@* |
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411 | ASSUME: A is a divisor on X which is linearly equivalent to an effective divisor. |
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412 | RETURN: divisor on X. |
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413 | THEORY: We compute an effective divisor linearly equivalent to A. |
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414 | KEYWORDS: divisors |
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415 | EXAMPLE: example effective; shows an example |
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416 | " |
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417 | { |
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418 | list LB = globalSections(A); |
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419 | if (size(LB[1])==0) {ERROR("the divisor is not linearly equivalent to an effective divisor");} |
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420 | ideal V = sectionIdeal(LB[1][1,1],LB[2],A); |
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421 | return(makeDivisor(V,ideal(1))); |
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422 | } |
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423 | example |
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424 | { "EXAMPLE:"; |
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425 | ring r=31991,(x,y,z),dp; |
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426 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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427 | qring Q = std(I); |
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428 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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429 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
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430 | divisor D = divisorplus(multdivisor(2,B),negativedivisor(A)); |
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431 | effective(D); |
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432 | } |
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433 | |
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434 | |
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435 | |
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436 | //////////////////////////////////////////////////////////////////////////////// |
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437 | // formal sums of divisors |
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438 | |
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439 | proc makeFormalDivisor(list L) |
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440 | "USAGE: makeFormalDivisor(L); L = list.@* |
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441 | ASSUME: L is a list of tuples of an integer and a divisor. |
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442 | RETURN: a formal divisor on X |
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443 | THEORY: Represents an integer formal sum of divisors. |
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444 | KEYWORDS: divisors |
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445 | EXAMPLE: example makeFormalDivisor; shows an example |
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446 | " |
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447 | { |
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448 | formaldivisor C; |
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449 | C.summands = L; |
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450 | return(C); |
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451 | } |
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452 | example |
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453 | { "EXAMPLE:"; |
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454 | ring r=31991,(x,y,z),dp; |
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455 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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456 | qring Q = std(I); |
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457 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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458 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
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459 | makeFormalDivisor(list(list(-5,A),list(2,B))); |
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460 | } |
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461 | |
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462 | |
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463 | proc evaluateFormalDivisor(formaldivisor D) |
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464 | "USAGE: evaluateFormalDivisor(D); D = formal divisor.@* |
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465 | ASSUME: D is a formal divisor on X. |
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466 | RETURN: a divisor on X |
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467 | THEORY: Will evaluate the formal sum. |
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468 | KEYWORDS: divisors |
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469 | EXAMPLE: example evaluateFormalDivisor; shows an example |
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470 | " |
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471 | { |
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472 | list L = D.summands; |
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473 | if (size(L)==0) {return(makeDivisor(ideal(1),ideal(1)));} |
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474 | int i; |
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475 | divisor E = multdivisor(L[1][1],L[1][2]); |
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476 | for ( i=2; i <= size(L); i++ ) |
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477 | { |
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478 | E = divisorplus(E, multdivisor(L[i][1],L[i][2])); |
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479 | } |
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480 | return(E); |
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481 | } |
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482 | example |
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483 | { "EXAMPLE:"; |
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484 | ring r=31991,(x,y,z),dp; |
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485 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
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486 | qring Q = std(I); |
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487 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
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488 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
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489 | formaldivisor fE= makeFormalDivisor(list(list(-5,A),list(2,B))); |
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490 | evaluateFormalDivisor(fE); |
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491 | } |
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492 | |
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493 | |
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494 | |
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495 | static proc position(divisor I,list L){ |
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496 | int i; |
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497 | for (i=1; i <=size(L); i++){ |
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498 | if (isEqualDivisor(I,L[i][2])==1) {return(i);} |
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499 | } |
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500 | return(0);} |
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501 | |
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502 | |
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503 | proc formaldivisorplus(formaldivisor A, formaldivisor B) |
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504 | "USAGE: formaldivisorplus(A ,B); A + B; A = formaldivisor, B = formaldivisor. @* |
---|
505 | ASSUME: A and B are formal divisors on X. |
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506 | RETURN: a formal divisor on X |
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507 | THEORY: The procedure will add the formal sums. |
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508 | KEYWORDS: divisors |
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509 | EXAMPLE: example formaldivisorplus; shows an example |
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510 | " |
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511 | { |
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512 | formaldivisor C; |
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513 | int i,p; |
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514 | int j=1; |
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515 | list L; |
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516 | list LA=A.summands; |
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517 | list LB=B.summands; |
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518 | for (i=1; i<=size(LA);i++){ |
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519 | p=position(LA[i][2],L); |
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520 | if (p==0) { |
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521 | L[j]=list(); |
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522 | L[j][2]=LA[i][2]; |
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523 | L[j][1]=LA[i][1]; |
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524 | j=j+1; |
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525 | } else { |
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526 | L[p][1]=L[p][1]+LA[i][1]; |
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527 | }; |
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528 | } |
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529 | for (i=1; i<=size(LB);i++){ |
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530 | p=position(LB[i][2],L); |
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531 | if (p==0) { |
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532 | L[j]=list(); |
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533 | L[j][2]=LB[i][2]; |
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534 | L[j][1]=LB[i][1]; |
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535 | j=j+1; |
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536 | } else { |
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537 | L[p][1]=L[p][1]+LB[i][1]; |
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538 | }; |
---|
539 | } |
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540 | //C.summands = (A.summands)+(B.summands); |
---|
541 | return(L); |
---|
542 | } |
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543 | example |
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544 | { "EXAMPLE:"; |
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545 | ring r=31991,(x,y,z),dp; |
---|
546 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
---|
547 | qring Q = std(I); |
---|
548 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
---|
549 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
---|
550 | divisor C = makeDivisor(ideal(x-z,y),ideal(1)); |
---|
551 | formaldivisor fE= makeFormalDivisor(list(list(-5,A),list(2,B))); |
---|
552 | formaldivisor fE2= makeFormalDivisor(list(list(-5,A),list(2,C))); |
---|
553 | formaldivisorplus(fE,fE2); |
---|
554 | } |
---|
555 | |
---|
556 | |
---|
557 | proc degreeFormalDivisor(formaldivisor A) |
---|
558 | "USAGE: degreeFormalDivisor(A); A = formaldivisor.@* |
---|
559 | ASSUME: A is a formaldivisor on X. |
---|
560 | RETURN: The degree of A. |
---|
561 | THEORY: We compute degrees of the summands and return the weighted sum. |
---|
562 | KEYWORDS: divisors |
---|
563 | EXAMPLE: example degreeFormalDivisor; shows an example |
---|
564 | " |
---|
565 | { |
---|
566 | int i,s; |
---|
567 | list L = A.summands; |
---|
568 | for (i=1;i<=size(L);i++){ |
---|
569 | s=s+L[i][1]*degreeDivisor(L[i][2]); |
---|
570 | } |
---|
571 | return(s); |
---|
572 | } |
---|
573 | example |
---|
574 | { "EXAMPLE:"; |
---|
575 | ring r=31991,(x,y,z),dp; |
---|
576 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
---|
577 | qring Q = std(I); |
---|
578 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
---|
579 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
---|
580 | formaldivisor fE= makeFormalDivisor(list(list(-5,A),list(2,B))); |
---|
581 | degreeFormalDivisor(fE); |
---|
582 | } |
---|
583 | |
---|
584 | |
---|
585 | proc multformaldivisor(int n,formaldivisor A) |
---|
586 | "USAGE: multformaldivisor(n ,A); A*n; n = integer, A = formaldivisor.@* |
---|
587 | ASSUME: n is an integer and A is a formal divisor on X. |
---|
588 | RETURN: a formal divisor on X |
---|
589 | THEORY: The procedure will multiply the formal sum with n. |
---|
590 | KEYWORDS: divisors |
---|
591 | EXAMPLE: example multformaldivisor; shows an example |
---|
592 | " |
---|
593 | { |
---|
594 | formaldivisor B; |
---|
595 | list L=A.summands; |
---|
596 | int i; |
---|
597 | for (i=1;i<=size(L);i++){ |
---|
598 | L[i][1]=n*L[i][1]; |
---|
599 | } |
---|
600 | B.summands=L; |
---|
601 | return(B); |
---|
602 | } |
---|
603 | example |
---|
604 | { "EXAMPLE:"; |
---|
605 | ring r=31991,(x,y,z),dp; |
---|
606 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
---|
607 | qring Q = std(I); |
---|
608 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
---|
609 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
---|
610 | formaldivisor fE= makeFormalDivisor(list(list(-5,A),list(2,B))); |
---|
611 | fE*2; |
---|
612 | } |
---|
613 | |
---|
614 | |
---|
615 | /*** |
---|
616 | * For operator overloading, which needs a procedure which takes a divisor first |
---|
617 | * and integer second. |
---|
618 | **/ |
---|
619 | proc proxymultformaldivisor(formaldivisor A, int n) |
---|
620 | { |
---|
621 | formaldivisor B; |
---|
622 | list L=A.summands; |
---|
623 | int i; |
---|
624 | for (i=1;i<=size(L);i++){ |
---|
625 | L[i][1]=n*L[i][1]; |
---|
626 | } |
---|
627 | B.summands=L; |
---|
628 | return(B); |
---|
629 | } |
---|
630 | |
---|
631 | |
---|
632 | |
---|
633 | proc negativeformaldivisor(formaldivisor A) |
---|
634 | "USAGE: negativeformaldivisor(A); A = formaldivisor.@* |
---|
635 | ASSUME: A is a formaldivisor on X. |
---|
636 | RETURN: a formal divisor on X |
---|
637 | THEORY: The procedure will change the signs of the coefficients. |
---|
638 | KEYWORDS: divisors |
---|
639 | EXAMPLE: example negativeformaldivisor; shows an example |
---|
640 | " |
---|
641 | { |
---|
642 | formaldivisor B; |
---|
643 | list L=A.summands; |
---|
644 | int i; |
---|
645 | for (i=1;i<=size(L);i++){ |
---|
646 | L[i][1]=-L[i][1]; |
---|
647 | } |
---|
648 | B.summands=L; |
---|
649 | return(B); |
---|
650 | } |
---|
651 | example |
---|
652 | { "EXAMPLE:"; |
---|
653 | ring r=31991,(x,y,z),dp; |
---|
654 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
---|
655 | qring Q = std(I); |
---|
656 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
---|
657 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
---|
658 | formaldivisor fE= makeFormalDivisor(list(list(-5,A),list(2,B))); |
---|
659 | negativeformaldivisor(fE); |
---|
660 | } |
---|
661 | |
---|
662 | |
---|
663 | static proc primDecDivisor(divisor D) |
---|
664 | "decompose a divisor into a formal divisor of primary divisors" |
---|
665 | { |
---|
666 | formaldivisor E; |
---|
667 | ideal I = D.num; |
---|
668 | ideal J = D.den; |
---|
669 | list L; |
---|
670 | int i; |
---|
671 | int j = 1; |
---|
672 | list LI = primdecGTZ(I); |
---|
673 | for (i=1;i<=size(LI);i++){ |
---|
674 | LI[i][2]; |
---|
675 | L[j]=list(1,makeDivisor(LI[i][1],ideal(1))); |
---|
676 | j=j+1; |
---|
677 | }; |
---|
678 | list LJ = primdecGTZ(J); |
---|
679 | for (i=1;i<=size(LJ);i++){ |
---|
680 | LJ[i][2]; |
---|
681 | L[j]=list(-1,makeDivisor(LJ[i][1],ideal(1))); |
---|
682 | j=j+1; |
---|
683 | }; |
---|
684 | E.summands=L; |
---|
685 | return(E);} |
---|
686 | |
---|
687 | |
---|
688 | |
---|
689 | |
---|
690 | //////////////////////////////////////////////////////////////////////////////// |
---|
691 | // P-divisors |
---|
692 | |
---|
693 | proc makePDivisor(list L) |
---|
694 | "USAGE: makePDivisor(L); L = list.@* |
---|
695 | ASSUME: L is a list of tuples of a integral polyhedron and a divisor such that |
---|
696 | all polyhedra have the same tail cone. |
---|
697 | RETURN: a pdivisor on X |
---|
698 | THEORY: Represents an polyhedral formal sum of divisors. |
---|
699 | KEYWORDS: divisors, polyhedra |
---|
700 | EXAMPLE: example makePDivisor; shows an example |
---|
701 | " |
---|
702 | { |
---|
703 | pdivisor P; |
---|
704 | list CP = decomposePolyhedron(L[1][1]); |
---|
705 | P.tail = CP[1]; |
---|
706 | list LP; |
---|
707 | LP[1]=list(CP[2],L[1][2]); |
---|
708 | int i; |
---|
709 | for (i=2; i<=size(L);i++){ |
---|
710 | CP = decomposePolyhedron(L[i][1]); |
---|
711 | if (!(CP[1]==P.tail)) {ERROR("All P-coefficients should have the same tail cone");} |
---|
712 | LP[i]=list(CP[2],L[i][2]); |
---|
713 | } |
---|
714 | P.summands = LP; |
---|
715 | return(P); |
---|
716 | } |
---|
717 | example |
---|
718 | { "EXAMPLE:"; |
---|
719 | ring r=31991,(x,y,z),dp; |
---|
720 | ideal I = y^2*z - x*(x-z)*(x+3*z); |
---|
721 | qring Q = std(I); |
---|
722 | divisor A = makeDivisor(ideal(x,z),ideal(1)); |
---|
723 | divisor B = makeDivisor(ideal(x,y),ideal(1)); |
---|
724 | intmat M[4][4]= 1,4,0,0, |
---|
725 | 1,0,3,0, |
---|
726 | 0,0,0,2, |
---|
727 | 1,1,1,1; |
---|
728 | polytope PP = polytopeViaPoints(M); |
---|
729 | makePDivisor(list(list(PP,A),list(PP,B))); |
---|
730 | } |
---|
731 | |
---|
732 | static proc decomposePolyhedron(polytope P){ |
---|
733 | bigintmat rays = vertices(P); |
---|
734 | bigintmat rays2 = rays; |
---|
735 | int i,j; |
---|
736 | for (i=1; i<=nrows(rays);i++){ |
---|
737 | if (rays[i,1]==1) { |
---|
738 | for (j=1; j<=ncols(rays);j++){ |
---|
739 | rays[i,j]=0; |
---|
740 | } |
---|
741 | } else { |
---|
742 | for (j=1; j<=ncols(rays);j++){ |
---|
743 | rays2[i,j]=0; |
---|
744 | } |
---|
745 | } |
---|
746 | } |
---|
747 | cone C = coneViaPoints(rays); |
---|
748 | polytope C2 = polytopeViaPoints(rays2); |
---|
749 | return(list(C,C2)); |
---|
750 | } |
---|
751 | |
---|
752 | |
---|
753 | |
---|