1 | /////////////////////////////////////////////////////////////////////////////// |
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2 | version="$Id: ncdecomp.lib,v 1.2 2004-06-01 13:53:35 levandov Exp $"; |
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3 | category="Noncommutative"; |
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4 | info=" |
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5 | LIBRARY: ncdecomp.lib Central character decomposition of a module |
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6 | AUTHORS: Viktor Levandovskyy, levandov@mathematik.uni-kl.de, |
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7 | @* Oleksandr Khomenko, Oleksandr.Khomenko@math.uni-freiburg.de. |
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8 | |
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9 | PROCEDURES: |
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10 | CentralQuot(I,G); for a module I and an ideal G, returns I:G, |
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11 | CentralSaturation(M,T); for a module M and an ideal T, returns M:T^{\infty}, |
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12 | CenCharDec(I,C); for a module I and a list C of generators of a center, returns a list L, where each entry consists of three records, namely |
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13 | L[*][1] is the character, L[*][2] is the Groebner basis of corresponding weight module, L[*][3] is the K-dimension of the weight module; |
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14 | "; |
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15 | |
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16 | LIB "ncalg.lib"; |
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17 | /////////////////////////////////////////////////////////////////////////////// |
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18 | static proc CharKernel(list L, int i) |
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19 | { |
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20 | // compute \cup L[j], j!=i |
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21 | int sL = size(L); |
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22 | if ( (i<=0) || (i>sL)) { return(0); } |
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23 | int j; |
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24 | list Li; |
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25 | if (i ==1 ) |
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26 | { |
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27 | Li = L[2..sL]; |
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28 | } |
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29 | if (i ==sL ) |
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30 | { |
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31 | Li = L[1..sL-1]; |
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32 | } |
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33 | if ( (i>1) && (i < sL)) |
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34 | { |
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35 | Li = L[1..i-1]; |
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36 | for (j=i+1; j<=sL; j++) |
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37 | { |
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38 | Li[j-1] = L[j]; |
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39 | } |
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40 | } |
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41 | // print("intersecting kernels..."); |
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42 | module Cres = intersect(Li[1..size(Li)]); |
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43 | return(Cres); |
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44 | } |
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45 | /////////////////////////////////////////////////////////////////////////////// |
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46 | static proc CentralQuotPoly(module M, poly g) |
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47 | { |
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48 | // here an elimination of components should be used ! |
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49 | int N=nrows(M); // M = A^N /I_M |
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50 | module @M; |
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51 | int i,j; |
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52 | for(i=1; i<=N; i++) |
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53 | { |
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54 | @M=@M,g*gen(i); |
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55 | } |
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56 | @M = simplify(@M,2); |
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57 | @M = @M,M; |
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58 | module S = syz(@M); |
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59 | matrix s = S; |
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60 | module T; |
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61 | vector t; |
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62 | for(i=1; i<=ncols(s); i++) |
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63 | { |
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64 | t = 0*gen(N); |
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65 | for(j=1; j<=N; j++) |
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66 | { |
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67 | t = t + s[j,i]*gen(j); |
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68 | } |
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69 | T[i] = t; |
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70 | } |
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71 | T = simplify(T,2); |
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72 | return(T); |
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73 | } |
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74 | /////////////////////////////////////////////////////////////////////////////// |
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75 | static proc MyIsEqual(module A, module B) |
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76 | { |
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77 | option(redSB); |
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78 | option(redTail); |
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79 | if (attrib(A,"isSB")!=1) |
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80 | { |
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81 | A = std(A); |
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82 | } |
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83 | if (attrib(B,"isSB")!=1) |
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84 | { |
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85 | B = std(B); |
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86 | } |
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87 | int ANSWER = 1; |
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88 | if ( ( ncols(A) == ncols(B) ) && ( nrows(A) == nrows(B) ) ) |
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89 | { |
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90 | module @AB = A-B; |
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91 | @AB = simplify(@AB,2); |
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92 | if (@AB[1]!=0) { ANSWER = 0; } |
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93 | } |
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94 | else { ANSWER = 0; } |
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95 | return(ANSWER); |
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96 | } |
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97 | /////////////////////////////////////////////////////////////////////////////// |
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98 | proc CentralQuot(module I, ideal G) |
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99 | "USAGE: CentralQuot(M, T), for a module M and an ideal T, |
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100 | RETURN: module of the central quotient I:G, |
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101 | NOTE: the output module is not necessarily a Groebner basis, |
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102 | SEE ALSO: CentralSaturation, CenCharDec |
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103 | EXAMPLE: example CentralQuot; shows examples |
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104 | "{ |
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105 | int i; |
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106 | list @L; |
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107 | for(i=1; i<=size(G); i++) |
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108 | { |
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109 | @L[i] = CentralQuotPoly(I,G[i]); |
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110 | } |
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111 | module @I = intersect(@L[1..size(G)]); |
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112 | if (nrows(@I)==1) |
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113 | { |
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114 | @I = ideal(@I); |
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115 | } |
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116 | return(@I); |
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117 | } |
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118 | example |
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119 | { "EXAMPLE:"; echo = 2; |
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120 | option(returnSB); |
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121 | def a = sl2(); |
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122 | setring a; |
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123 | ideal I = e3,f3,h3-4*h; |
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124 | I = std(I); |
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125 | poly C=4*e*f+h^2-2*h; |
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126 | ideal G = (C-8)*(C-24); |
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127 | ideal R = CentralQuot(I,G); |
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128 | R; |
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129 | } |
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130 | /////////////////////////////////////////////////////////////////////////////// |
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131 | proc CentralSaturation(module M, ideal T) |
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132 | "USAGE: CentralSaturation(M, T), for a module M and an ideal T, |
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133 | RETURN: module of the central saturation M:T^{\infty}, |
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134 | NOTE: the output module is not necessarily a Groebner basis, |
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135 | SEE ALSO: CentralQuot, CenCharDec |
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136 | EXAMPLE: example CentralSaturation; shows examples |
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137 | "{ |
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138 | option(redSB); |
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139 | option(redTail); |
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140 | option(returnSB); |
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141 | module Q=0; |
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142 | module S=M; |
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143 | while ( !MyIsEqual(Q,S) ) |
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144 | { |
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145 | Q = CentralQuot(M, T); |
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146 | S = CentralQuot(Q, T); |
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147 | } |
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148 | if (nrows(Q)==1) |
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149 | { |
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150 | Q = ideal(Q); |
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151 | } |
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152 | // Q = std(Q); |
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153 | return(Q); |
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154 | } |
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155 | example |
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156 | { "EXAMPLE:"; echo = 2; |
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157 | option(returnSB); |
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158 | def a = sl2(); |
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159 | setring a; |
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160 | ideal I = e3,f3,h3-4*h; |
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161 | I = std(I); |
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162 | poly C=4*e*f+h^2-2*h; |
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163 | ideal G = C*(C-8); |
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164 | ideal R = CentralSaturation(I,G); |
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165 | R=std(R); |
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166 | vdim(R); |
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167 | R; |
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168 | } |
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169 | /////////////////////////////////////////////////////////////////////////////// |
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170 | proc CenCharDec(ideal I, list Center) |
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171 | "USAGE: CenCharDec(I, L), I an ideal and Center a list of generators of the center; |
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172 | RETURN: a list L, where each entry consists of three records, namely |
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173 | L[*][1] is the character, L[*][2] is the Groebner basis of corresponding weight module, L[*][3] is the K-dimension of the weight module; |
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174 | NOTE: |
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175 | SEE ALSO: CentralQuot, CentralSaturation |
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176 | EXAMPLE: example CenCharDec; shows examples |
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177 | " |
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178 | { |
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179 | // M = A/I |
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180 | //1. Find the Zariski closure of Supp_Z M |
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181 | // J = Ann_M 1 == I |
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182 | // J \cap Z: |
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183 | option(redSB); |
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184 | option(redTail); |
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185 | option(returnSB); |
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186 | def @A = basering; |
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187 | setring @A; |
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188 | int sZ=size(Center); |
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189 | int i,j; |
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190 | poly t=1; |
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191 | for(i=1; i<=nvars(@A); i++) |
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192 | { |
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193 | t=t*var(i); |
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194 | } |
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195 | ring @Z=0,(@z(1..sZ)),dp; |
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196 | // @Z; |
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197 | def @ZplusA = @A+@Z; |
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198 | setring @ZplusA; |
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199 | // @ZplusA; |
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200 | ideal I = imap(@A,I); |
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201 | list Center = imap(@A,Center); |
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202 | poly t = imap(@A,t); |
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203 | ideal @Ker; |
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204 | for(i=1; i<=sZ; i++) |
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205 | { |
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206 | @Ker[i]=@z(i) - Center[i]; |
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207 | } |
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208 | @Ker = @Ker,I; |
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209 | ideal @JcapZ = eliminate(@Ker,t); |
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210 | // do not forget parameters of a basering! |
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211 | string strZ="ring @@Z=("+charstr(@A)+"),(@z(1.."+string(sZ)+")),dp;"; |
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212 | // print(strZ); |
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213 | execute(strZ); |
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214 | setring @@Z; |
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215 | ideal @JcapZ = imap(@ZplusA,@JcapZ); |
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216 | @JcapZ = std(@JcapZ); |
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217 | // @JcapZ; |
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218 | int sJ = vdim(@JcapZ); |
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219 | if (sJ==-1) |
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220 | { |
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221 | "There is no finite decomposition"; |
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222 | return(0); |
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223 | } |
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224 | // print(@JcapZ); |
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225 | // 2. compute the min.ass.primes of the ideal in the center |
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226 | LIB "primdec.lib"; |
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227 | list @L = minAssGTZ(@JcapZ); |
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228 | int sL = size(@L); |
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229 | list @CharKer; |
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230 | for(i=1; i<=sL; i++) |
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231 | { |
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232 | @L[i] = std(@L[i]); |
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233 | } |
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234 | // print("etL:"); |
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235 | // @L; |
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236 | // 3. compute the intersections of characters |
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237 | for(i=1; i<=sL; i++) |
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238 | { |
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239 | @CharKer[i] = CharKernel(@L,i); |
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240 | } |
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241 | // print("Charker:"); |
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242 | // @CharKer; |
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243 | // 4. Go back to the algebra and compute central saturations |
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244 | setring @A; |
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245 | map @M = @@Z,Center[1..size(Center)]; |
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246 | list L = @M(@CharKer); |
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247 | list R,@R; |
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248 | for(i=1; i<=sL; i++) |
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249 | { |
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250 | @R[1] = L[i]; |
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251 | @R[2] = CentralSaturation(I,L[i]); |
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252 | if (nrows(@R[2])==1) |
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253 | { |
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254 | @R[2] = ideal(@R[2]); |
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255 | } |
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256 | @R[2] = std(@R[2]); |
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257 | @R[3] = vdim(@R[2]); |
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258 | R[i] = @R; |
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259 | } |
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260 | return(R); |
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261 | } |
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262 | example |
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263 | { "EXAMPLE:"; echo = 2; |
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264 | |
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265 | option(returnSB); |
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266 | def a = sl2(); |
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267 | setring a; |
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268 | ideal I = e3,f3,h3-4*h; |
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269 | I = twostd(I); |
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270 | poly C=4*e*f+h^2-2*h; |
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271 | list T = CenCharDec(I,C); |
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272 | T; |
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273 | } |
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