1 | version="$Id: nchomolog.lib,v 1.3 2005-06-07 10:24:46 Singular Exp $"; |
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2 | category="Noncommutative"; |
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3 | info=" |
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4 | LIBRARY: nchomolog.lib Procedures for Noncommutative Homological Algebra |
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5 | AUTHORS: Viktor Levandovskyy levandov@mathematik.uni-kl.de, |
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6 | Gerhard Pfister, pfister@mathematik.uni-kl.de |
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7 | |
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8 | PROCEDURES: |
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9 | ncExt_R(k,M); Ext^k(M',R), M module, R basering, M'=coker(M) |
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10 | ncExt(k,M,N); Ext^k(M',N'), M,N modules, M'=coker(M), N'=coker(N) |
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11 | ncHom(M,N); Hom(M',N'), M,N modules, M'=coker(M), N'=coker(N) |
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12 | coHom(A,k); Hom(R^k,A), A matrix over basering R |
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13 | contraHom(A,k); Hom(A,R^k), A matrix over basering R |
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14 | tensorMaps(M,N); tensor product of matrices |
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15 | ncTensorMod(M,N); Tensor product of modules M'=coker(M), N'=coker(N) |
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16 | ncTor(k,M,N); Tor_k(M',N'), M,N modules, M'=coker(M), N'=coker(N) |
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17 | "; |
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18 | |
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19 | LIB "gkdim.lib"; |
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20 | LIB "involut.lib"; |
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21 | |
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22 | proc contraHom(matrix M, int s) |
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23 | { |
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24 | int n,m=ncols(M),nrows(M); |
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25 | int a,b,c; |
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26 | matrix R[s*n][s*m]; |
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27 | for(b=1; b<=m; b++) |
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28 | { |
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29 | for(a=1; a<=s; a++) |
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30 | { |
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31 | for(c=1; c<=n; c++) |
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32 | { |
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33 | R[(a-1)*n+c,(a-1)*m+b] = M[b,c]; |
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34 | } |
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35 | } |
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36 | } |
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37 | return(R); |
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38 | } |
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39 | example |
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40 | { "EXAMPLE:"; echo = 2; |
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41 | ring A=0,(x,y,z),dp; |
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42 | matrix M[3][3]=1,2,3, |
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43 | 4,5,6, |
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44 | 7,8,9; |
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45 | module cM = contraHom(M,2); |
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46 | print(cM); |
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47 | } |
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48 | |
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49 | proc coHom(matrix M, int s) |
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50 | { |
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51 | int n,m=ncols(M),nrows(M); |
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52 | int a,b,c; |
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53 | matrix R[s*m][s*n]; |
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54 | for(b=1; b<=s; b++) |
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55 | { |
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56 | for(a=1; a<=m; a++) |
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57 | { |
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58 | for(c=1; c<=n; c++) |
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59 | { |
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60 | R[(a-1)*s+b,(c-1)*s+b] = M[a,c]; |
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61 | } |
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62 | } |
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63 | } |
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64 | return(R); |
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65 | } |
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66 | example |
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67 | { "EXAMPLE:"; echo = 2; |
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68 | ring A=0,(x,y,z),dp; |
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69 | matrix M[3][3]=1,2,3, |
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70 | 4,5,6, |
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71 | 7,8,9; |
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72 | module cM = coHom(M,2); |
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73 | print(cM); |
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74 | } |
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75 | |
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76 | proc ncHom(matrix M, matrix N) |
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77 | "USAGE: ncHom(M,N); M,N modules |
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78 | COMPUTE: A presentation of Hom(M',N'), M'=coker(M), N'=coker(N) |
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79 | ASSUME: M' is a left module, N' is a centralizing bimodule |
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80 | NOTE: ncHom(M,N) is a right module, hence a right presentation matrix |
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81 | is returned |
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82 | EXAMPLE: example ncHom; shows examples |
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83 | " |
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84 | { |
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85 | // assume: M is left module |
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86 | // assume: N is centralizing bimodule |
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87 | // returns a right presentation matrix |
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88 | // for a right module |
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89 | matrix F = contraHom(M,nrows(N)); |
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90 | matrix B = coHom(N,ncols(M)); |
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91 | matrix C = coHom(N,nrows(M)); |
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92 | def Rbase = basering; |
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93 | def Rop = opposite(Rbase); |
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94 | setring Rop; |
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95 | matrix Bop = oppose(Rbase, B); |
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96 | matrix Cop = oppose(Rbase, C); |
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97 | matrix Fop = oppose(Rbase, F); |
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98 | matrix Dop = modulo(Fop, Bop); |
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99 | matrix Eop = modulo(Dop, Cop); |
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100 | setring Rbase; |
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101 | matrix E = oppose(Rop, Eop); |
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102 | kill Rop; |
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103 | return(E); |
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104 | } |
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105 | example |
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106 | { "EXAMPLE:"; echo = 2; |
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107 | ring A=0,(x,y,z),dp; |
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108 | matrix M[3][3]=1,2,3, |
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109 | 4,5,6, |
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110 | 7,8,9; |
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111 | matrix N[2][2]=x,y, |
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112 | z,0; |
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113 | module H = ncHom(M,N); |
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114 | print(H); |
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115 | } |
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116 | |
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117 | proc ncExt(int i, matrix Ps, matrix Ph) |
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118 | "USAGE: Ext(i,M,N); i int, M,N modules |
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119 | COMPUTE: A presentation of Ext^i(M',N'); for M'=coker(M) and N'=coker(N). |
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120 | NOTE: ncExt(M,N) is a right module, hence a right presentation matrix |
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121 | is returned |
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122 | EXAMPLE: example ncExt; shows examples |
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123 | " |
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124 | { |
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125 | if(i==0) { return(module(ncHom(Ps,Ph))); } |
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126 | list Phi = mres(Ps,i+1); |
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127 | module Im = coHom(Ph,ncols(Phi[i+1])); |
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128 | module f = contraHom(matrix(Phi[i+1]),nrows(Ph)); |
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129 | module Im1 = coHom(Ph,ncols(Phi[i])); |
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130 | module Im2 = contraHom(matrix(Phi[i]),nrows(Ph)); |
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131 | def Rbase = basering; |
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132 | def Rop = opposite(Rbase); |
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133 | setring Rop; |
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134 | module fop = oppose(Rbase,f); |
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135 | module Imop = oppose(Rbase,Im); |
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136 | module Im1op = oppose(Rbase,Im1); |
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137 | module Im2op = oppose(Rbase,Im2); |
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138 | module ker_op = modulo(fop,Imop); |
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139 | module ext_op = modulo(ker_op,Im1op+Im2op); |
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140 | // ext = prune(ext); |
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141 | // to be discussed and done prune_from_the_left |
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142 | setring Rbase; |
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143 | module ext = oppose(Rop,ext_op); |
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144 | kill Rop; |
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145 | return(ext); |
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146 | } |
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147 | example |
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148 | { "EXAMPLE:"; echo = 2; |
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149 | ring R = 0,(x,y),dp; |
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150 | ideal I = x2-y3; |
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151 | qring S = std(I); |
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152 | module M = [-x,y],[-y2,x]; |
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153 | module E1 = ncExt(1,M,M); |
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154 | E1; |
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155 | } |
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156 | |
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157 | |
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158 | proc ncExt_R(int i, matrix Ps) |
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159 | "USAGE: ncExt_R(i, M); i int, M module |
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160 | COMPUTE: a presentation of Ext^i(M',R); for M'=coker(M). |
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161 | RETURN: right module Ext, a presentation of Ext^i(M',R) |
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162 | EXAMPLE: example ncExt_R; shows an example |
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163 | " |
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164 | { |
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165 | if (i==0) |
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166 | { // return the formal adjoint (== the dual) |
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167 | matrix Ret = transpose(Ps); |
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168 | def Rbase = basering; |
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169 | def Rop = opposite(Rbase); |
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170 | setring Rop; |
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171 | module Retop = oppose(Rbase,Ret); |
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172 | // "Computing prune of Hom"; |
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173 | // Retop = prune(Retop); |
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174 | // Retop = std(Retop); |
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175 | setring Rbase; |
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176 | Ret = oppose(Rop, Retop); |
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177 | kill Rop; |
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178 | return(Ret); |
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179 | } |
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180 | list Phi = mres(Ps,i+1); |
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181 | module f = transpose(matrix(Phi[i+1])); |
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182 | module Im2 = transpose(matrix(Phi[i])); |
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183 | def Rbase = basering; |
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184 | def Rop = opposite(Rbase); |
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185 | setring Rop; |
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186 | module fop = oppose(Rbase,f); |
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187 | module Im2op = oppose(Rbase,Im2); |
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188 | module ker_op = modulo(fop,std(0)); |
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189 | module ext_op = modulo(ker_op,Im2op); |
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190 | // ext = prune(ext); |
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191 | // to be discussed and done prune_from_the_left |
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192 | // necessary: compute SB! |
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193 | // "Computing SB of Ext"; |
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194 | option(redSB); |
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195 | option(redTail); |
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196 | ext_op = std(ext_op); |
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197 | int dimop = GKdim(ext_op); |
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198 | printf("Ext has dimension %s",dimop); |
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199 | if (dimop==0) |
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200 | { |
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201 | printf("of K-dimension %s",vdim(ext_op)); |
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202 | } |
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203 | setring Rbase; |
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204 | module ext = oppose(Rop,ext_op); // a right module! |
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205 | kill Rop; |
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206 | return(ext); |
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207 | } |
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208 | example |
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209 | { "EXAMPLE:"; echo = 2; |
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210 | ring R = 0,(x,y),dp; |
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211 | ideal I = x2-y3; |
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212 | qring S = std(I); |
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213 | module M = [-x,y],[-y2,x]; |
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214 | module E1 = ncExt(1,M,M); |
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215 | E1; |
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216 | } |
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217 | |
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218 | proc altExt_R(int i, matrix Ps, map Invo) |
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219 | // TODO!!!!!!!! |
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220 | // matrix Ph |
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221 | // work thru Involutions; |
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222 | { |
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223 | if(i==0) |
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224 | { // return the formal adjoint |
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225 | matrix Ret = transpose(Ps); |
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226 | matrix Retop = involution(Ret, Invo); |
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227 | // "Computing prune of Hom"; |
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228 | // Retop = prune(Retop); |
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229 | // Retop = std(Retop); |
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230 | return(Retop); |
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231 | } |
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232 | list Phi = mres(Ps,i+1); |
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233 | // module Im = coHom(Ph,ncols(Phi[i+1])); |
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234 | module f = transpose(matrix(Phi[i+1])); |
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235 | f = involution(f, Invo); |
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236 | //= contraHom(matrix(Phi[i+1]),nrows(Ph)); |
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237 | // module Im1 = coHom(Ph,ncols(Phi[i])); |
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238 | module Im2 = transpose(matrix(Phi[i])); |
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239 | Im2 = involution(Im2, Invo); |
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240 | //contraHom(matrix(Phi[i]),nrows(Ph)); |
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241 | module ker_op = modulo(f,std(0)); |
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242 | module ext_op = modulo(ker_op,Im2); |
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243 | // ext = prune(ext); |
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244 | // to be discussed and done prune_from_the_left |
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245 | // optionally: compute SB! |
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246 | // "Computing prune of Ext"; |
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247 | ext_op = std(ext_op); |
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248 | int dimop = GKdim(ext_op); |
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249 | printf("Ext has dimension %s",dimop); |
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250 | if (dimop==0) |
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251 | { |
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252 | printf("of K-dimension %s",vdim(ext_op)); |
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253 | } |
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254 | module ext = involution(ext_op, Invo); // what about transpose? |
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255 | return(ext); |
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256 | } |
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257 | example |
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258 | { "EXAMPLE:"; echo = 2; |
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259 | ring R = 0,(x,y),dp; |
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260 | ideal I = x2-y3; |
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261 | qring S = std(I); |
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262 | module M = [-x,y],[-y2,x]; |
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263 | module E1 = ncExt(1,M,M); |
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264 | E1; |
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265 | } |
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266 | |
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267 | proc tensorMaps(matrix M, matrix N) |
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268 | { |
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269 | int r = ncols(M); |
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270 | int s = nrows(M); |
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271 | int p = ncols(N); |
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272 | int q = nrows(N); |
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273 | int a,b,c,d; |
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274 | matrix R[s*q][r*p]; |
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275 | for(b=1;b<=p;b++) |
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276 | { |
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277 | for(d=1;d<=q;d++) |
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278 | { |
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279 | for(a=1;a<=r;a++) |
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280 | { |
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281 | for(c=1;c<=s;c++) |
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282 | { |
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283 | R[(c-1)*q+d,(a-1)*p+b]=M[c,a]*N[d,b]; |
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284 | } |
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285 | } |
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286 | } |
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287 | } |
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288 | return(R); |
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289 | } |
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290 | |
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291 | proc ncTensorMod(matrix Phi, matrix Psi) |
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292 | { |
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293 | int s=nrows(Phi); |
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294 | int q=nrows(Psi); |
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295 | matrix A=tensorMaps(unitmat(s),Psi); //I_s tensor Psi |
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296 | matrix B=tensorMaps(Phi,unitmat(q)); //Phi tensor I_q |
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297 | matrix R=concat(A,B); //sum of A and B |
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298 | return(R); |
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299 | } |
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300 | |
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301 | |
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302 | proc ncTor(int i, matrix Ps, matrix Ph) |
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303 | { |
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304 | if(i==0) { return(module(ncTensorMod(Ps,Ph))); } |
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305 | // the tensor product |
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306 | list Phi = mres(Ph,i+1); // a resolution of Ph |
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307 | module Im = tensorMaps(unitmat(nrows(Phi[i])),Ps); |
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308 | module f = tensorMaps(matrix(Phi[i]),unitmat(nrows(Ps))); |
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309 | module Im1 = tensorMaps(unitmat(ncols(Phi[i])),Ps); |
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310 | module Im2 = tensorMaps(matrix(Phi[i+1]),unitmat(nrows(Ps))); |
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311 | module ker = modulo(f,Im); |
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312 | module tor = modulo(ker,Im1+Im2); |
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313 | // tor = prune(tor); |
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314 | return(tor); |
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315 | } |
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316 | |
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317 | proc Hochschild() |
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318 | { |
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319 | ring A = 0,(x,y),dp; |
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320 | ideal I = x2-y3; |
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321 | qring B = std(I); |
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322 | module M = [-x,y],[-y2,x]; |
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323 | ring C = 0,(x,y,z,w),dp; // x->z, y->w |
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324 | ideal I = x2-y3,z3-w2; |
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325 | qring Be = std(I); //the enveloping algebra |
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326 | matrix AA[1][2] = x-z,y-w; //the presentation of the algebra B as Be-module |
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327 | module MM = imap(B,M); |
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328 | module E = ncExt(1,AA,MM); |
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329 | print(E); //the presentation of the H^1(A,M) |
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330 | |
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331 | |
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332 | ring A = 0,(x,y),dp; |
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333 | ideal I = x2-y3; |
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334 | qring B = std(I); |
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335 | ring C = 0,(x,y,z,w),dp; |
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336 | ideal I = x2-y3,z3-w2; |
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337 | qring Be = std(I); //the enveloping algebra |
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338 | matrix AA[1][2] = x-z,y-w; //the presentation of B as Be-module |
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339 | matrix AAA[1][2] = z,w; // equivalent? pres. of B |
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340 | print(ncExt(1,AA,AA)); //the presentation of the H^1(A,A) |
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341 | print(ncExt(1,AAA,AAA)); |
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342 | } |
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343 | |
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344 | proc Lie() |
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345 | { |
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346 | // consider U(sl2)* U(sl2)^opp; |
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347 | LIB "ncalg.lib"; |
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348 | ring A = 0,(e,f,h,H,F,E),Dp; // any degree ordering |
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349 | int N = 6; // nvars(A); |
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350 | matrix @D[N][N]; |
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351 | @D[1,2] = -h; |
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352 | @D[1,3] = 2*e; |
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353 | @D[2,3] = -2*f; |
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354 | @D[4,5] = 2*F; |
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355 | @D[4,6] = -2*E; |
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356 | @D[5,6] = H; |
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357 | ncalgebra(1,@D); |
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358 | ideal Q = E,F,H; |
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359 | poly Z = 4*e*f+h^2-2*h; // center |
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360 | poly Zo = 4*F*E+H^2+2*H; // center opposed |
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361 | ideal Qe = Z,Zo; |
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362 | //qring B = twostd(Qe); |
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363 | //ideal T = e-E,f-F,h-H; |
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364 | //ideal T2 = e-H,f-F,h-E; |
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365 | //Q = twostd(Q); // U is U(sl2) as left U(sl2)* U(sl2)^opp -- module |
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366 | matrix M[1][3] = E,F,H; |
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367 | module X0 = ncExt(0,M,M); |
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368 | print(X0); |
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369 | |
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370 | module X1 = ncExt(1,M,M); |
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371 | print(X1); |
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372 | module X2 = ncExt(2,M,M); // equal to Tor^Z_1(K,K) |
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373 | print(X2); |
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374 | |
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375 | |
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376 | // compute Tor^Z_1(K,K) |
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377 | |
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378 | ring r = 0,(z),dp; |
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379 | ideal i = z; |
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380 | matrix I[1][1]=z; |
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381 | Tor(1,I,I); |
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382 | } |
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383 | |
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384 | |
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385 | proc AllExts(module N, list #) |
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386 | // computes and shows everything |
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387 | // assumes we are in the opposite |
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388 | // and N is dual of some M |
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389 | // if # is given, map Invo and Ext_Invo are used |
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390 | { |
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391 | int UseInvo = 0; |
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392 | int sl = size(#); |
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393 | if (sl >0) |
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394 | { |
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395 | ideal I = ideal(#[1]); |
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396 | map Invo = basering, I; |
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397 | UseInvo = 1; |
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398 | "Using the involution"; |
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399 | } |
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400 | int nv = nvars(basering); |
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401 | int i,d; |
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402 | module E; |
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403 | list EE; |
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404 | print("--- module:"); print(matrix(N)); |
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405 | for (i=1; i<=nv; i++) |
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406 | { |
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407 | if (UseInvo) |
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408 | { |
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409 | E = altExt_R(i,N,Invo); |
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410 | } |
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411 | else |
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412 | { |
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413 | E = ncExt_R(i,N); |
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414 | } |
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415 | printf("--- Ext %s",i); |
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416 | print(matrix(E)); |
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417 | EE[i] = E; |
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418 | } |
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419 | // return(E); |
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420 | } |
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