1 | version="$Id$"; |
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2 | category="Algebraic Geometry"; |
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3 | info=" |
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4 | LIBRARY: resjung.lib Resolution of surface singularities (Desingularization) |
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5 | by Jung's Algorithm |
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6 | AUTHORS: Philipp Renner, philipp_renner@web.de |
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7 | @* Anne Fruehbis-Krueger, anne@math.uni-hannover.de |
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8 | OVERVIEW: This library implements resolution of singularities by Jung's algorithm, |
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9 | @* which is only applicable to surfaces and persues the following strategy: |
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10 | @* 1) project surface to the plane |
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11 | @* 2) resolve singularities of the branch locus |
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12 | @* 3) pull-back the original surface by this resolution morphism |
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13 | @* 4) normalize the resulting surface so that the remaining singularities |
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14 | @* are of Hirzebruch-Jung type |
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15 | @* 5) resolve Hirzebruch-Jung singularities explicitly |
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16 | @* Currently, the Hirzebruch-Jung singularities are resolved by calling |
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17 | @* the procedure resolve from the library resolve.lib, because this is not |
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18 | @* overly expensive and the original last step of Jung's algorithm is not |
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19 | @* implemented yet. |
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20 | REFERENCES: |
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21 | [1] Jung, H.: Darstellung der Funktionen eines algebraischen Koerpers zweier unabhaengigen |
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22 | Veraenderlichen x,y in der Umgebung x=a, y= b, Journal fuer Reine und Angewandte Mathematik |
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23 | 133,289-314 (1908) |
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24 | @* (the origin of this method) |
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25 | @*[2] J.Kollar: Lectures on Resolution of Singularities, Princeton University Press (2007) |
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26 | @* (contains large overview over various known methods for curves and surfaces as well as |
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27 | a detailed description of the approach in the general case) |
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28 | |
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29 | PROCEDURES: |
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30 | jungresolve(J,i) computes a resolution of the surface given by the |
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31 | ideal J using Jungs Method |
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32 | |
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33 | clocus(J) computes the critical locus of the projection of V(J) |
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34 | onto the coordinate plane of the last two coordinates |
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35 | embR(C) computes a strong embedded resolution of the plane curve V(C) |
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36 | jungnormal(J,i) computes intermediate step in Jung's algorithm |
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37 | such that all singularities are of Hirzebruch-Jung type |
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38 | "; |
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39 | |
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40 | LIB "resolve.lib"; |
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41 | LIB "mregular.lib"; |
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42 | LIB "sing.lib"; |
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43 | LIB "normal.lib"; |
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44 | LIB "primdec.lib"; |
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45 | |
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46 | ////////////////////////////////////////////////////////////////////////////// |
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47 | //---------------------------------------------------------------------------- |
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48 | //Critical locus for the Weierstrass map induced by the noether normalization |
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49 | //---------------------------------------------------------------------------- |
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50 | proc clocus(ideal id) |
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51 | "USAGE: clocus(ideal J); |
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52 | @* J = ideal |
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53 | ASSUME: J = two dimensional ideal in noether position with respect |
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54 | to the last two variables |
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55 | RETURN: A ring containing the ideal Clocus respresenting the critical |
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56 | locus of the projection V(J)-->C^2 onto the coordinate plane |
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57 | of the last two coordinates |
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58 | EXAMPLE: example clocus; shows an example |
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59 | " |
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60 | { |
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61 | def A = basering; |
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62 | int n = nvars(A); |
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63 | list l = equidim(id); |
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64 | int i,j; |
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65 | int k = size(l); |
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66 | ideal LastTwo = var(n-1),var(n); |
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67 | ideal lowdim = 1; //the components of id with dimension smaller 2 |
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68 | if(k>1){ |
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69 | for(j=1;j<k;j++){ |
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70 | lowdim = intersect(lowdim,l[j]); |
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71 | } |
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72 | } |
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73 | //lowdim = radical(lowdim); // affects performance |
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74 | ideal I = l[size(l)]; |
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75 | poly product=1; |
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76 | kill l; |
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77 | for(i=1; i < n-1; i++){ |
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78 | //elimination of all variables exept var(i),var(n-1),var(n) |
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79 | intvec v; |
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80 | for(j=1; j < n-1; j++){ |
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81 | if(j<>i){ |
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82 | v[j]=1; |
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83 | } |
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84 | else{ |
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85 | v[j]=0; |
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86 | } |
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87 | } |
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88 | v[size(v)+1]=0; |
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89 | v[size(v)+1]=0; |
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90 | if(defined(ringl)) {kill ringl;} |
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91 | list ringl = ringlist(A); |
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92 | list l; |
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93 | l[1] = "a"; |
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94 | l[2] = v; |
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95 | list ll = insert(ringl[3],l); |
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96 | ringl[3]=ll; |
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97 | kill l,ll; |
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98 | def R = ring(ringl); //now x_j > x_i > x_n-1 > x_n forall j != i,n-1,n |
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99 | setring R; |
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100 | ideal J = groebner(fetch(A,I)); //this eliminates the variables |
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101 | setring A; |
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102 | ideal J = fetch(R,J); |
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103 | attrib(J,"isPrincipal",0); |
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104 | if(size(J)==1){ |
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105 | attrib(J,"isPrincipal",1); |
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106 | } |
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107 | int index = 1; |
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108 | if(attrib(J,"isPrincipal")==0){ |
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109 | setring R; |
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110 | for(j = 1;j<=size(J);j++){ //determines the monic polynomial |
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111 | //in var(i) with coefficents in C2 |
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112 | if(defined(w)) {kill w;} |
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113 | intvec w = leadexp(J[j]); |
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114 | attrib(w,"isMonic",1); |
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115 | for(k = 1;k<=size(w);k++){ |
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116 | if(w[k] <> 0 && k <> i){ |
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117 | attrib(w,"isMonic",0); |
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118 | break; |
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119 | } |
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120 | } |
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121 | if(attrib(w,"isMonic")==1){ |
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122 | index = j; |
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123 | break; |
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124 | } |
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125 | kill w; |
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126 | } |
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127 | setring A; |
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128 | } |
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129 | product = product*resultant(J[index],diff(J[index],var(i)),var(i)); |
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130 | //Product of the discriminants, which lies in C2 |
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131 | kill index,J,v; |
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132 | } |
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133 | ring C2 = 0,(var(n-1),var(n)),dp; |
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134 | setring C2; |
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135 | ideal Clocus = imap(A,product); //the critical locus is contained in this |
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136 | ideal I = preimage(A,LastTwo,lowdim); |
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137 | Clocus = radical(intersect(Clocus,I)); //radical is necessary since the |
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138 | //resultant is not reduced in general |
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139 | export(Clocus); |
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140 | return(C2); |
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141 | } |
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142 | example |
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143 | {"EXAMPLE:"; |
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144 | echo = 2; |
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145 | ring R=0,(x,y,z),dp; |
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146 | ideal I=x2-y3z3; |
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147 | list li=clocus(I); |
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148 | def S=li[1]; |
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149 | setring S; |
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150 | Clocus; |
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151 | } |
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152 | /////////////////////////////////////////////////////////////////////////////// |
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153 | //----------------------------------------------------------------------------- |
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154 | // Build the fibre product of the embedded resolution and |
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155 | // the coordinate ring of the variety |
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156 | //----------------------------------------------------------------------------- |
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157 | static proc buildFP(list embR,ideal NoetherN, map phi){ |
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158 | def A = basering; |
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159 | int i,j,k; |
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160 | list fibreP; |
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161 | int n = nvars(A); |
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162 | for(i=1;i<=size(embR);i++){ |
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163 | if(defined(R)) {kill R;} |
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164 | def R = embR[i]; |
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165 | setring R; |
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166 | list temp = ringlist(A); |
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167 | // create data for the new ring |
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168 | // e.g. if A=K[x_1,..,x_n] and R=K[y_1,..,y_m], K[x_1,..,x_n-2,y_1,..,y_m] |
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169 | for(j = 1; j<= nvars(R);j++){ |
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170 | string st = string(var(j)); |
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171 | temp[2][n-2+j] = st; |
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172 | kill st; |
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173 | } |
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174 | temp[4] = BO[1]; |
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175 | ideal J = BO[5]; //ideal of the resolution map |
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176 | export(J); |
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177 | int m = size(J); |
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178 | def R2 = ring(temp); |
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179 | kill temp; |
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180 | setring R2; |
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181 | ideal Temp=0; //defines map from R to R2 which is the inclusion |
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182 | for(k=n-1;k<n-1+nvars(R);k++){ |
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183 | Temp = Temp + ideal(var(k)); |
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184 | } |
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185 | map f = R,Temp; |
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186 | kill Temp; |
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187 | ideal FibPMI = ideal(0); //defines the map from A to R2 |
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188 | for(k=1;k<=nvars(A)-m;k++){ |
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189 | FibPMI=FibPMI+var(k); |
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190 | } |
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191 | FibPMI= FibPMI+ideal(f(J)); |
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192 | map FibMap = A,FibPMI; |
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193 | kill f,FibPMI; |
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194 | ideal TotalT = groebner(FibMap(NoetherN)); |
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195 | ideal QIdeal = TotalT; |
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196 | export(QIdeal); |
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197 | ideal FibPMap = ideal(FibMap(phi)); |
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198 | ideal BMap = FibPMap; |
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199 | export(BMap); |
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200 | fibreP[i] = R2; |
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201 | setring R; |
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202 | kill J,R,R2,m; |
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203 | } |
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204 | return(fibreP); |
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205 | }; |
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206 | |
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207 | /////////////////////////////////////////////////////////////////////////////// |
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208 | //----------------------------------------------------------------------------- |
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209 | // embedded resolution for curves -- optimized for our situation |
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210 | //----------------------------------------------------------------------------- |
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211 | proc embR(ideal C) |
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212 | "USAGE: embR(ideal C); |
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213 | @* C = ideal |
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214 | ASSUME: C = ideal of plane curve |
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215 | RETURN: a list l of rings |
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216 | l[i] is a ring containing a basic object BO, the result of the |
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217 | resolution. |
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218 | THEORY: Given a plain curve C, an embedded resolution of this curve |
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219 | @* by means of a sequence of blow ups at singular points of C is |
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220 | @* computed such that the resulting total transform consists |
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221 | @* of non-singular components and only has strict normal crossings. |
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222 | @* The result of each blow up is represented by means of |
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223 | @* affine charts and hence also the final result is represented in |
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224 | @* charts, which are collected in a list l of rings. Each ring |
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225 | @* in this list corresponds to one chart. The collection of |
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226 | @* data describing the ambient space, the strict transform, the |
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227 | @* exceptional divisors and the combination of the blow ups |
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228 | @* leading to this chart is contained in the list BO which resides |
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229 | @* in this ring. |
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230 | NOTE: - The best way to look at the data contained in BO is the |
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231 | @* procedure showBO from the library resolve.lib. |
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232 | @* - The algorithm does not touch normal crossings of V(C). |
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233 | EXAMPLE: example embR; shows an example |
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234 | " |
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235 | { |
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236 | ideal J = 1; |
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237 | attrib(J,"iswholeRing",1); |
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238 | list primdec = equidim(C); |
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239 | if(size(primdec)==2){ |
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240 | // zero dimensional components of the discrimiant curve |
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241 | // are smooth an cross normally so they can be ignored |
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242 | // in the resolution process |
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243 | ideal Lowdim = radical(primdec[1]); |
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244 | } |
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245 | else{ |
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246 | J=radical(C); |
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247 | } |
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248 | kill primdec; |
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249 | list l; |
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250 | list BO = createBO(J,l); |
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251 | kill J,l; |
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252 | list result = resolve2(BO); |
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253 | if(defined(Lowdim)){ |
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254 | for(int i = 1;i<=size(result);i++){ |
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255 | // had zero dimensional components which are now added to the end result |
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256 | if(defined(R)) {kill R;} |
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257 | def R = result[i]; |
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258 | setring R; |
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259 | map f = R2,BO[5]; |
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260 | BO[2]=BO[2]*f(Lowdim); |
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261 | kill R,f; |
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262 | } |
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263 | } |
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264 | return(result); |
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265 | } |
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266 | example |
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267 | {"EXAMPLE:"; |
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268 | echo=2; |
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269 | ring R=0,(x,y),dp; |
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270 | ideal C=x2-y3; |
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271 | list li=embR(C); |
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272 | def S=li[1]; |
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273 | setring S; |
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274 | showBO(BO); |
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275 | } |
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276 | /////////////////////////////////////////////////////////////////////////////// |
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277 | static proc resolve2(list BO){ |
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278 | // computes an embedded resolution for the basic object BO |
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279 | // and returns a list of rings with BO -- specifically optimized |
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280 | // to our situation |
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281 | def H = basering; |
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282 | int i,j,k; |
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283 | setring H; attrib(BO[2],"smoothC",0); |
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284 | export(BO); |
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285 | list result; |
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286 | result[1]=H; |
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287 | attrib(result[1],"isResolved",0); // has only simple normal crossings |
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288 | attrib(result[1],"smoothC",0); // has smooth components |
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289 | int safety=0; // number of runs restricted to 30 |
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290 | while(1){ |
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291 | int count2 = 0; // counts the number of smooth charts |
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292 | int p = size(result); |
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293 | for(j = 1;j<=p;j++){ |
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294 | if(attrib(result[j],"isResolved")==0){ |
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295 | if(defined(R)){kill R;} |
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296 | def R = result[j]; |
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297 | setring R; |
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298 | if(attrib(result[j],"smoothC")==0){ |
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299 | // has possibly singular components so choose a singular point and blow up |
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300 | list primdecPC = primdecGTZ(BO[2]); |
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301 | attrib(result[j],"smoothC",1); |
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302 | for(i = 1;i<=size(primdecPC);i++){ |
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303 | ideal Sl = groebner(slocus(primdecPC[i][2])); |
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304 | if(deg(NF(1,Sl))!=-1){ |
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305 | list primdecSL = primdecGTZ(Sl); |
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306 | for(int h =1;h<=size(primdecSL);h++){ |
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307 | attrib(primdecSL[h],"isRational",1); |
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308 | } |
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309 | kill h; |
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310 | if(!defined(index)){int index = 1;} |
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311 | if(defined(blowup)){kill blowup;} |
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312 | list blowup = blowUpBO(BO,primdecSL[index][2],3); |
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313 | // if it has only a rational singularity, blow it up, |
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314 | // else choose some arbitary singular point |
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315 | if(attrib(primdecSL[1],"isRational")==0){ |
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316 | // if we blew up a non rational singularity, the exeptional divisors |
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317 | // are reduzible, so we need to separate them |
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318 | for(k=1;k<=size(blowup);k++){ |
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319 | def R2=blowup[k]; |
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320 | setring R2; |
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321 | list L; |
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322 | for(int l = 1;l<=size(BO[4]);l++){ |
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323 | list primdecED=primdecGTZ(BO[4][l]); |
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324 | L = L + primdecED; |
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325 | kill primdecED; |
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326 | } |
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327 | kill l; |
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328 | BO[4] = L; |
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329 | blowup[k]=R2; |
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330 | kill L,R2; |
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331 | } |
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332 | } |
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333 | kill primdecSL; |
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334 | list hlp; |
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335 | for(k = 1;k<j;k++){ |
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336 | hlp[k]=result[k]; |
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337 | attrib(hlp[k],"isResolved",attrib(result[k],"isResolved")); |
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338 | attrib(hlp[k],"smoothC",attrib(result[k],"smoothC")); |
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339 | } |
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340 | for(k =1;k<=size(blowup);k++){ |
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341 | hlp[size(hlp)+1]=blowup[k]; |
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342 | attrib(hlp[size(hlp)],"isResolved",0); |
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343 | attrib(hlp[size(hlp)],"smoothC",0); |
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344 | } |
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345 | for(k = j+1;k<=size(result);k++){ |
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346 | hlp[size(hlp)+1]=result[k]; |
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347 | attrib(hlp[size(hlp)],"isResolved",attrib(result[k],"isResolved")); |
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348 | attrib(hlp[size(hlp)],"smoothC",attrib(result[k],"smoothC")); |
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349 | } |
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350 | result = hlp; |
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351 | kill hlp; |
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352 | i=size(primdecPC); |
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353 | } |
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354 | else{ |
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355 | attrib(result[j],"smoothC",1); |
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356 | } |
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357 | kill Sl; |
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358 | } |
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359 | kill primdecPC; |
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360 | j=p; |
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361 | break; |
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362 | } |
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363 | else{ |
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364 | // if it has smooth components, determine all the intersection points |
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365 | // and check whether they are snc or not |
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366 | int count = 0; |
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367 | ideal Collect = BO[2]; |
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368 | for(i = 1;i<=size(BO[4]);i++){ |
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369 | Collect = Collect*BO[4][i]; |
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370 | } |
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371 | list primdecSL = primdecGTZ(slocus(Collect)); |
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372 | for(k = 1;k<=size(primdecSL);k++){ |
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373 | attrib(primdecSL[k],"isRational",1); |
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374 | } |
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375 | if(defined(blowup)){kill blowup;} |
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376 | list blowup = blowUpBO(BO,primdecSL[1][2],3); |
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377 | if(attrib(primdecSL[1],"isRational")==0){ |
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378 | for(k=1;k<=size(blowup);k++){ |
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379 | def R2=blowup[k]; |
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380 | setring R2; |
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381 | list L; |
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382 | for(int l = 1;l<=size(BO[4]);l++){ |
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383 | list primdecED=primdecGTZ(BO[4][l]); |
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384 | L = L + primdecED; |
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385 | kill primdecED; |
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386 | } |
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387 | kill l; |
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388 | BO[4] = L; |
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389 | blowup[k]=R2; |
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390 | kill L,R2; |
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391 | } |
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392 | } |
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393 | kill Collect; |
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394 | for(i=1;i<=size(primdecSL);i++){ |
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395 | list L = BO[4]; |
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396 | L[size(L)+1]=BO[2]; |
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397 | for(int l = 1;l<=size(L);l++){ |
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398 | if(L[l][1]==1){L=delete(L,l);} |
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399 | } |
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400 | kill l; |
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401 | if(normalCrossing(ideal(0),L,primdecSL[i][2])==0){ |
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402 | if(defined(blowup)){kill blowup;} |
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403 | list blowup = blowUpBO(BO,primdecSL[i][2],3); |
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404 | list hlp; |
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405 | for(k = 1;k<j;k++){ |
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406 | hlp[k]=result[k]; |
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407 | attrib(hlp[k],"isResolved",attrib(result[k],"isResolved")); |
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408 | attrib(hlp[k],"smoothC",attrib(result[k],"smoothC")); |
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409 | } |
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410 | for(k =1;k<=size(blowup);k++){ |
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411 | hlp[size(hlp)+1]=blowup[k]; |
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412 | attrib(hlp[size(hlp)],"isResolved",0); |
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413 | attrib(hlp[size(hlp)],"smoothC",1); |
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414 | } |
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415 | for(k = j+1;k<=size(result);k++){ |
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416 | hlp[size(hlp)+1]=result[k]; |
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417 | attrib(hlp[size(hlp)],"isResolved",attrib(result[k],"isResolved")); |
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418 | attrib(hlp[size(hlp)],"smoothC",attrib(result[k],"smoothC")); |
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419 | } |
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420 | result = hlp; |
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421 | kill hlp; |
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422 | j = p; |
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423 | break; |
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424 | } |
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425 | else{ |
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426 | count++; |
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427 | } |
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428 | kill L; |
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429 | } |
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430 | if(count == size(primdecSL)){ |
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431 | attrib(result[j],"isResolved",1); |
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432 | } |
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433 | kill count,primdecSL; |
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434 | } |
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435 | kill R; |
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436 | } |
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437 | else{ |
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438 | count2++; |
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439 | } |
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440 | } |
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441 | if(count2==size(result)){ |
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442 | break; |
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443 | } |
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444 | kill count2,p; |
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445 | safety++; |
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446 | } |
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447 | return(result); |
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448 | }; |
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449 | /////////////////////////////////////////////////////////////////////////////// |
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450 | static proc jungfib(ideal id, int noeth) |
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451 | "USAGE: jungfib(ideal J, int i); |
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452 | @* J = ideal |
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453 | @* i = int |
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454 | ASSUME: J = two dimensional ideal |
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455 | RETURN: a list l of rings |
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456 | l[i] is a ring containing two Ideals: QIdeal and BMap. |
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457 | BMap defines a birational morphism from V(QIdeal)-->V(J), such that |
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458 | V(QIdeal) has only quasi-ordinary singularities. |
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459 | If i!=0 then it's assumed that J is in noether position with respect |
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460 | to the last two variables. |
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461 | If i=0 the algorithm computes a coordinate change such that J is in |
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462 | noether position. |
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463 | EXAMPLE: none, as it is a static procedure |
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464 | " |
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465 | { |
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466 | int i; |
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467 | if(!defined(noeth)){ |
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468 | int noeth = 0; |
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469 | } |
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470 | if(noeth <> 1){print("//WARNING: Noether normalization can make the algorithm unstable");} |
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471 | ideal I = std(radical(id)); |
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472 | def A = basering; |
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473 | int n = nvars(A); |
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474 | if(deg(NF(1,groebner(slocus(id)))) == -1){ |
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475 | list result; |
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476 | ideal QIdeal = I; |
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477 | ideal BMap = maxideal(1); |
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478 | export(QIdeal); |
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479 | export(BMap); |
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480 | result[1] = A; |
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481 | return(result); |
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482 | } |
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483 | if(char(A) <> 0){ERROR("only works for characterisitc 0");} //dummy check |
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484 | if(dim(I)<> 2){ERROR("dimension is unequal 2");} //dummy check |
---|
485 | |
---|
486 | // Noether Normalization |
---|
487 | if(noeth == 0){ |
---|
488 | if(n==3){ |
---|
489 | int pos = NoetherP_test(I); |
---|
490 | if(pos ==0){ |
---|
491 | if(size(I) == 1){ |
---|
492 | ideal noethpos = var(1)+var(3),var(2)+var(3),var(3); |
---|
493 | } |
---|
494 | else{ |
---|
495 | ideal noethpos = NoetherPosition(I); |
---|
496 | } |
---|
497 | map phi = A,noethpos; |
---|
498 | kill noethpos; |
---|
499 | } |
---|
500 | else{ |
---|
501 | ideal NoetherPos = var(pos); |
---|
502 | for(i = 1;i<=3;i++){ |
---|
503 | if(i<>pos){ |
---|
504 | NoetherPos = NoetherPos + var(i); |
---|
505 | } |
---|
506 | } |
---|
507 | map phi = A,NoetherPos; |
---|
508 | kill i,pos,NoetherPos; |
---|
509 | } |
---|
510 | } |
---|
511 | else{ |
---|
512 | map phi = A,NoetherPosition(I); |
---|
513 | } |
---|
514 | ideal NoetherN = ideal(phi(I)); |
---|
515 | //image of id under the NoetherN coordinate change |
---|
516 | } |
---|
517 | else{ |
---|
518 | ideal NoetherN = I; |
---|
519 | map phi = A,maxideal(1); |
---|
520 | } |
---|
521 | kill I; |
---|
522 | //Critical Locus |
---|
523 | def C2 = clocus(NoetherN); |
---|
524 | setring C2; |
---|
525 | |
---|
526 | //dim of critical locus is 0 then the normalization is an resolution |
---|
527 | if(dim(Clocus) == 0){ |
---|
528 | setring A; |
---|
529 | list nor = normal(NoetherN); |
---|
530 | list result; |
---|
531 | for(i = 1;i<=size(nor[1]);i++){ |
---|
532 | def R = nor[1][i]; |
---|
533 | setring R; |
---|
534 | ideal QIdeal = norid; |
---|
535 | ideal BMap = BMap; |
---|
536 | export(QIdeal); |
---|
537 | export(BMap); |
---|
538 | result[size(result)+1] = R; |
---|
539 | kill R; |
---|
540 | } |
---|
541 | print("This is a resolution."); |
---|
542 | return(result); |
---|
543 | } |
---|
544 | |
---|
545 | // dim of critical locus is 1, so compute embedded resolution of the discriminant curve |
---|
546 | list embRe = embR(Clocus); |
---|
547 | |
---|
548 | // build the fibreproduct |
---|
549 | setring A; |
---|
550 | list fibreP = buildFP(embRe,NoetherN,phi); |
---|
551 | // a list of lists, where fibreP[i] contains the information |
---|
552 | // concerning the i-th chart of the fibrepoduct |
---|
553 | // fibreP[i] is the ring; QIdeal the quotientideal; BMap is the map from A |
---|
554 | return(fibreP); |
---|
555 | } |
---|
556 | /////////////////////////////////////////////////////////////////////////////// |
---|
557 | |
---|
558 | proc jungnormal(ideal id,int noeth) |
---|
559 | "USAGE: jungnormal(ideal J, int i); |
---|
560 | @* J = ideal |
---|
561 | @* i = int |
---|
562 | ASSUME: J = two dimensional ideal |
---|
563 | RETURN: a list l of rings |
---|
564 | l[k] is a ring containing two Ideals: QIdeal and BMap. |
---|
565 | BMap defines a birational morphism from V(QIdeal)-->V(J), such that |
---|
566 | V(QIdeal) has only singularities of Hizebuch-Jung type. |
---|
567 | If i!=0 then it's assumed that J is in noether position with respect |
---|
568 | to the last two variables. |
---|
569 | If i=0 the algorithm computes a coordinate change such that J is in |
---|
570 | noether position. |
---|
571 | EXAMPLE: example jungnormal; shows an example |
---|
572 | " |
---|
573 | { |
---|
574 | def A = basering; |
---|
575 | list fibreP = jungfib(id,noeth); |
---|
576 | list result; |
---|
577 | int i,j; |
---|
578 | for(i =1;i<=size(fibreP);i++){ |
---|
579 | def R1 = fibreP[i]; |
---|
580 | setring R1; |
---|
581 | map f1 = A,BMap; |
---|
582 | def nor = normal(QIdeal); |
---|
583 | for(j = 1;j<=size(nor[1]);j++){ |
---|
584 | def R2 = nor[1][j]; |
---|
585 | setring R2; |
---|
586 | map f2 = R1,normap; |
---|
587 | ideal BMap = ideal(f2(f1)); |
---|
588 | ideal QIdeal = norid; |
---|
589 | export(BMap); |
---|
590 | export(QIdeal); |
---|
591 | result[size(result)+1] = R2; |
---|
592 | setring R1; |
---|
593 | kill R2; |
---|
594 | } |
---|
595 | kill R1; |
---|
596 | } |
---|
597 | return(result); |
---|
598 | } |
---|
599 | example |
---|
600 | {"EXAMPLE:"; |
---|
601 | echo = 2; |
---|
602 | ring R=0,(x,y,z),dp; |
---|
603 | ideal J=x2+y3z3; |
---|
604 | list li=jungnormal(J,1); |
---|
605 | li; |
---|
606 | def S=li[1]; |
---|
607 | setring S; |
---|
608 | QIdeal; |
---|
609 | BMap; |
---|
610 | } |
---|
611 | /////////////////////////////////////////////////////////////////////////////// |
---|
612 | |
---|
613 | proc jungresolve(ideal id,int noeth) |
---|
614 | "USAGE: jungresolve(ideal J, int i); |
---|
615 | @* J = ideal |
---|
616 | @* i = int |
---|
617 | ASSUME: J = two dimensional ideal |
---|
618 | RETURN: a list l of rings |
---|
619 | l[k] is a ring containing two Ideals: QIdeal and BMap. |
---|
620 | BMap defines a birational morphism from V(QIdeal)-->V(J), such that |
---|
621 | V(QIdeal) is smooth. For this the algorithm computes first |
---|
622 | a representation of V(J) with Hirzebruch-Jung singularities |
---|
623 | and then it currently uses Villamayor's algorithm to resolve |
---|
624 | these singularities. |
---|
625 | If i!=0 then it's assumed that J is in noether position with respect |
---|
626 | to the last two variables. |
---|
627 | If i=0 the algorithm computes a coordinate change such that J is in |
---|
628 | noether position. |
---|
629 | EXAMPLE: example jungresolve; shows an example |
---|
630 | " |
---|
631 | { |
---|
632 | def A = basering; |
---|
633 | list result; |
---|
634 | int i,j; |
---|
635 | list nor = jungnormal(id,noeth); |
---|
636 | for(i = 1;i<=size(nor);i++){ |
---|
637 | if(defined(R)){kill R;} |
---|
638 | def R3 = nor[i]; |
---|
639 | setring R3; |
---|
640 | def R = changeord("dp"); |
---|
641 | setring R; |
---|
642 | ideal QIdeal = imap(R3,QIdeal); |
---|
643 | ideal BMap = imap(R3,BMap); |
---|
644 | map f = A,BMap; |
---|
645 | if(QIdeal <> 0){ |
---|
646 | list res = resolve(QIdeal); |
---|
647 | for(j =1;j<=size(res[1]);j++){ |
---|
648 | def R2 = res[1][j]; |
---|
649 | setring R2; |
---|
650 | if(defined(QIdeal)){kill QIdeal;} |
---|
651 | if(defined(BMap)){kill BMap;} |
---|
652 | if(BO[1]<>0){ideal QIdeal = BO[1]+BO[2];} |
---|
653 | else{ideal QIdeal = BO[2];} |
---|
654 | map g = R,BO[5]; |
---|
655 | ideal BMap = ideal(g(f)); |
---|
656 | export(QIdeal); |
---|
657 | export(BMap); |
---|
658 | result[size(result)+1] = R2; |
---|
659 | kill R2; |
---|
660 | } |
---|
661 | kill res; |
---|
662 | } |
---|
663 | else{ |
---|
664 | result[size(result)+1] = nor[i]; |
---|
665 | } |
---|
666 | kill R,R3; |
---|
667 | } |
---|
668 | return(result); |
---|
669 | } |
---|
670 | example |
---|
671 | {"EXAMPLE:"; |
---|
672 | echo = 2; |
---|
673 | ring R=0,(x,y,z),dp; |
---|
674 | ideal J=x2+y3z3+y2z5; |
---|
675 | list li=jungresolve(J,1); |
---|
676 | li; |
---|
677 | def S=li[1]; |
---|
678 | setring S; |
---|
679 | QIdeal; |
---|
680 | BMap; |
---|
681 | } |
---|
682 | /////////////////////////////////////////////////////////////////////////////// |
---|
683 | static proc NoetherP_test(ideal id){ |
---|
684 | def A = basering; |
---|
685 | list ringA=ringlist(A); |
---|
686 | int i,j,k; |
---|
687 | int index = 0; |
---|
688 | if(size(id)==1 && nvars(A)){ // test if V(id) = C[x,y,z]/<f> |
---|
689 | list L; |
---|
690 | intvec v = 1,1,1; |
---|
691 | L[1] = "lp"; |
---|
692 | L[2] = v; |
---|
693 | kill v; |
---|
694 | poly f = id[1]; |
---|
695 | for(i = 1;i<=3;i++){ |
---|
696 | setring A; |
---|
697 | list l = ringA; //change ordering to lp and var(i)>var(j) j!=i |
---|
698 | list vari = ringA[2]; |
---|
699 | string h = vari[1]; |
---|
700 | vari[1] = vari[i]; |
---|
701 | vari[i] = h; |
---|
702 | l[2] = vari; |
---|
703 | kill h,vari; |
---|
704 | l[3][1] = L; |
---|
705 | def R = ring(l); |
---|
706 | kill l; |
---|
707 | setring R; |
---|
708 | ideal I = imap(A,id); |
---|
709 | if(defined(v)){kill v;} |
---|
710 | intvec v = leadexp(I[1]); |
---|
711 | attrib(v,"isMonic",1); |
---|
712 | for(k = 2;k<=3;k++){ |
---|
713 | // checks whether f is monic in var(i) |
---|
714 | if(v[k] <> 0 || v[1] == 0){ |
---|
715 | attrib(v,"isMonic",0); |
---|
716 | j++; |
---|
717 | break; |
---|
718 | } |
---|
719 | } |
---|
720 | if(attrib(v,"isMonic")==1){ |
---|
721 | index = i; |
---|
722 | return(index); |
---|
723 | } |
---|
724 | kill R; |
---|
725 | } |
---|
726 | if(j == 3){ |
---|
727 | return(0); |
---|
728 | } |
---|
729 | } |
---|
730 | else{ |
---|
731 | // not yet a test for more variables |
---|
732 | return(index); |
---|
733 | } |
---|
734 | } |
---|
735 | ///////////////////////////////////////////////////////////////////////// |
---|
736 | //// copied from resolve.lib, deleting parts of procedures which are /// |
---|
737 | //// not necessary in this setting /// |
---|
738 | ///////////////////////////////////////////////////////////////////////// |
---|
739 | static proc normalCrossing(ideal J,list E,ideal V) |
---|
740 | "Internal procedure - no help and no example available |
---|
741 | " |
---|
742 | { |
---|
743 | int i,d,j; |
---|
744 | int n=nvars(basering); |
---|
745 | list E1,E2; |
---|
746 | ideal K,M,Estd; |
---|
747 | intvec v,w; |
---|
748 | |
---|
749 | for(i=1;i<=size(E);i++) |
---|
750 | { |
---|
751 | Estd=std(E[i]+J); |
---|
752 | if(deg(Estd[1])>0) |
---|
753 | { |
---|
754 | E1[size(E1)+1]=Estd; |
---|
755 | } |
---|
756 | } |
---|
757 | E=E1; |
---|
758 | for(i=1;i<=size(E);i++) |
---|
759 | { |
---|
760 | v=i; |
---|
761 | E1[i]=list(E[i],v); |
---|
762 | } |
---|
763 | list ll; |
---|
764 | int re=1; |
---|
765 | |
---|
766 | while((size(E1)>0)&&(re==1)) |
---|
767 | { |
---|
768 | K=E1[1][1]; |
---|
769 | v=E1[1][2]; |
---|
770 | attrib(K,"isSB",1); |
---|
771 | E1=delete(E1,1); |
---|
772 | d=n-dim(K); |
---|
773 | M=minor(jacob(K),d)+K; |
---|
774 | if(deg(std(M+V)[1])>0) |
---|
775 | { |
---|
776 | re=0; |
---|
777 | break; |
---|
778 | } |
---|
779 | for(i=1;i<=size(E);i++) |
---|
780 | { |
---|
781 | for(j=1;j<=size(v);j++){if(v[j]==i){break;}} |
---|
782 | if(j<=size(v)){if(v[j]==i){i++;continue;}} |
---|
783 | Estd=std(K+E[i]); |
---|
784 | w=v; |
---|
785 | if(deg(Estd[1])==0){i++;continue;} |
---|
786 | if(d==n-dim(Estd)) |
---|
787 | { |
---|
788 | if(deg(std(Estd+V)[1])>0) |
---|
789 | { |
---|
790 | re=0; |
---|
791 | break; |
---|
792 | } |
---|
793 | } |
---|
794 | w[size(w)+1]=i; |
---|
795 | E2[size(E2)+1]=list(Estd,w); |
---|
796 | } |
---|
797 | if(size(E2)>0) |
---|
798 | { |
---|
799 | if(size(E1)>0) |
---|
800 | { |
---|
801 | E1[size(E1)+1..size(E1)+size(E2)]=E2[1..size(E2)]; |
---|
802 | } |
---|
803 | else |
---|
804 | { |
---|
805 | E1=E2; |
---|
806 | } |
---|
807 | } |
---|
808 | kill E2; |
---|
809 | list E2; |
---|
810 | } |
---|
811 | return(re); |
---|
812 | } |
---|
813 | ////////////////////////////////////////////////////////////////////////////// |
---|
814 | |
---|
815 | static proc zariski(ideal id){ |
---|
816 | def A = basering; |
---|
817 | ideal QIdeal = std(id); |
---|
818 | ideal BMap= maxideal(1); |
---|
819 | export(BMap); |
---|
820 | int i,j; |
---|
821 | export(QIdeal); |
---|
822 | if(dim(QIdeal)<>2){ |
---|
823 | print("wrong dimension"); |
---|
824 | list result; |
---|
825 | return(result); |
---|
826 | } |
---|
827 | list result; |
---|
828 | result[1]= A; |
---|
829 | attrib(result[1],"isSmooth",0); |
---|
830 | while(1){ |
---|
831 | if(defined(count)){kill count;} |
---|
832 | int count =0; |
---|
833 | for(i = 1;i<= size(result);i++){ |
---|
834 | attrib(result[i],"isSmooth",1); |
---|
835 | def R = result[i]; |
---|
836 | setring R; |
---|
837 | if(!defined(Slocus)){ |
---|
838 | if(QIdeal[1] == 0){ |
---|
839 | ideal Slocus = 1; |
---|
840 | } |
---|
841 | else{ |
---|
842 | ideal Slocus = std(slocus(QIdeal)); |
---|
843 | } |
---|
844 | } |
---|
845 | if(NF(1,Slocus)<>0){ |
---|
846 | attrib(result[i],"isSmooth",0); |
---|
847 | } |
---|
848 | else{ |
---|
849 | count++; |
---|
850 | } |
---|
851 | kill R; |
---|
852 | } |
---|
853 | if(count == size(result)){return(result);} |
---|
854 | count = 0; |
---|
855 | list hlp; |
---|
856 | for(i = 1;i<=size(result);i++){ |
---|
857 | if(attrib(result[i],"isSmooth")==1){ |
---|
858 | hlp[size(hlp)+1] = result[i]; |
---|
859 | attrib(hlp[size(hlp)],"isSmooth",attrib(result[i],"isSmooth")); |
---|
860 | count++; |
---|
861 | i++; |
---|
862 | continue; |
---|
863 | } |
---|
864 | def R = result[i]; |
---|
865 | setring R; |
---|
866 | //print(N1); |
---|
867 | list nor = normal(QIdeal); |
---|
868 | //print(N2); |
---|
869 | for(j = 1;j<= size(nor[1]);j++){ |
---|
870 | def R3 = nor[1][j]; |
---|
871 | setring R3; |
---|
872 | def R2 = changeord("dp"); |
---|
873 | setring R2; |
---|
874 | ideal norid = imap(R3,norid); |
---|
875 | ideal normap = imap(R3,normap); |
---|
876 | kill R3; |
---|
877 | map f = R,normap; |
---|
878 | if(defined(BMap)){kill BMap;} |
---|
879 | if(defined(QIdeal)){kill QIdeal;} |
---|
880 | ideal BMap = f(BMap); |
---|
881 | ideal QIdeal = norid; |
---|
882 | export(BMap); |
---|
883 | export(QIdeal); |
---|
884 | if(QIdeal[1]<> 0){ |
---|
885 | ideal Slocus = slocus(QIdeal); |
---|
886 | Slocus = std(radical(Slocus)); |
---|
887 | } |
---|
888 | else{ |
---|
889 | ideal Slocus = 1; |
---|
890 | } |
---|
891 | if(NF(1,Slocus)<> 0){ |
---|
892 | list blowup = blowUp(norid,Slocus); |
---|
893 | for(int k = 1;k<=size(blowup);k++){ |
---|
894 | def R3 = blowup[k]; |
---|
895 | setring R3; |
---|
896 | ideal QIdeal = sT + aS; |
---|
897 | map f = R2,bM; |
---|
898 | ideal BMap = f(BMap); |
---|
899 | export(BMap); |
---|
900 | export(QIdeal); |
---|
901 | hlp[size(hlp)+1] = R3; |
---|
902 | attrib(hlp[size(hlp)],"isSmooth",0); |
---|
903 | kill R3; |
---|
904 | } |
---|
905 | kill k,blowup; |
---|
906 | } |
---|
907 | else{ |
---|
908 | hlp[size(hlp)+1] = R2; |
---|
909 | attrib(hlp[size(hlp)],"isSmooth",1); |
---|
910 | } |
---|
911 | kill R2; |
---|
912 | } |
---|
913 | kill R,j,nor; |
---|
914 | } |
---|
915 | kill i; |
---|
916 | if(count == size(result)){ |
---|
917 | return(result); |
---|
918 | } |
---|
919 | else{ |
---|
920 | result = hlp; |
---|
921 | attrib(result,"isSmooth",0); |
---|
922 | kill hlp; |
---|
923 | } |
---|
924 | } |
---|
925 | } |
---|
926 | ////////////////////////////////////////////////////////////////////////////// |
---|
927 | // End of copied part and edited part from resolve.lib |
---|
928 | ////////////////////////////////////////////////////////////////////////////// |
---|
929 | |
---|