1 | ///////////////////////////////////////////////////////////////////////////// |
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2 | //procedures examples comments |
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3 | version="$Id$"; |
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4 | category="Noncommutative"; |
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5 | info=" |
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6 | LIBRARY: purityfiltration.lib Algorithms for computing a purity filtration of a given module |
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7 | |
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8 | AUTHORS: Christian Schilli, christian.schilli@rwth-aachen.de |
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9 | @* Viktor Levandovskyy, levandov@math.rwth-aachen.de |
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10 | |
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11 | |
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12 | OVERVIEW: |
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13 | Purity is a notion with several meanings. In our context it is equidimensionality |
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14 | @* of a module (that is all M is pure iff any nonzero submodule of N has the same dimension as N). |
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15 | @* Notably, one should define purity with respect to a given dimension function. In the context |
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16 | @* of this library the corresponding function is the homological grade number j_A(M) of a module M over |
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17 | @* an K-algebra A. j_A(M) is the minimal integer k, such that Ext^k_A(M,A) != 0. |
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18 | |
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19 | REFERENCES: [AQ] Alban Quadrat: Grade filtration of linear functional systems, INRIA Report 7769 (2010), to appear in Acta Applicanda Mathematica. |
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20 | @* [B93] Jan-Erik Bjoerk: Analytic D-modules and applications, Kluwer Acad. Publ., 1993. |
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21 | @* [MB10] Mohamed Barakat: Purity Filtration and the Fine Structure of Autonomy. Proc. MTNS, 2010. |
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22 | |
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23 | PROCEDURES: |
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24 | projectiveDimension(matrix T,int i); compute a shortest resolution of coker(T) and its projective dimension |
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25 | purityFiltration(matrix R); compute the purity filtration of coker(R) |
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26 | purityTriang(matrix R) compute a triangular blockmatrix T, such that coker(R) isomorphic to coker(T) |
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27 | gradeNumber(matrix R); gives the grade number of the module coker(R) |
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28 | showgrades(list T); gives all grade numbers of the modules represented by the elements of T |
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29 | allExtOfLeft(matrix R); computes all right ext-modules ext^i(M,D) of a left module M=coker(R) over the ring D |
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30 | allExtOfRight(matrix R); computes all left ext-modules ext^i(M,D) of a right module M=coker(R) over the ring D |
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31 | doubleExt(matrix R, int i); computes the left module ext^i(ext^i(M,D),D) over the ring D, M=coker(R) |
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32 | allDoubleExt(matrix R); computes all double ext modules ext^i(ext^j(M,D),D) of the left module coker(R) over the ring D |
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33 | is_pure(matrix R); checks whether the module coker(R) is pure |
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34 | purelist(list T); checks whether all the modules represented by the elements of T are pure |
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35 | |
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36 | KEYWORDS: D-module; ext-module; filtration; projective dimension; resolution; purity |
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37 | "; |
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38 | |
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39 | LIB "nctools.lib"; |
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40 | LIB "matrix.lib"; |
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41 | LIB "poly.lib"; |
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42 | LIB "general.lib"; |
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43 | LIB "control.lib"; |
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44 | LIB "nchomolog.lib"; |
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45 | |
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46 | //------------------- auxiliary procedures -------------------------- |
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47 | |
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48 | proc testPurityfiltrationLib() |
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49 | { |
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50 | example projectiveDimension; |
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51 | example purityFiltration; |
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52 | example purityTriang; |
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53 | example gradeNumber; |
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54 | example showgrades; |
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55 | example allExtOfLeft; |
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56 | example allExtOfRight; |
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57 | example doubleExt; |
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58 | example allDoubleExt; |
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59 | example is_pure; |
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60 | example purelist; |
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61 | } |
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62 | |
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63 | static proc iszero (matrix R) |
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64 | "USAGE: iszero(R); R a matrix |
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65 | RETURN: int, 1, if R is zero, |
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66 | @* or 0, if it's not |
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67 | PURPOSE: checks, if the matrix R is zero or not |
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68 | " |
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69 | { |
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70 | ideal i=R; |
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71 | i=std(i); |
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72 | if (i==0) |
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73 | { |
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74 | return (1); |
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75 | } |
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76 | return (0); |
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77 | } |
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78 | |
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79 | proc lsyz (matrix R) |
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80 | "USAGE: lsyz(R), R a matrix |
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81 | RETURN: matrix, a left syzygy of R |
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82 | PURPOSE: computes the left syzygy module of the module, generated by the rows of R, i.e. |
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83 | @* a matrix X with X*R=0 |
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84 | " |
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85 | { |
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86 | matrix L=transpose(syz(transpose(R))); |
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87 | return(L); |
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88 | } |
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89 | |
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90 | proc rsyz (matrix R) |
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91 | "USAGE: rsyz(R), R a matrix |
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92 | RETURN: matrix, a rightsyzygy of R |
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93 | PURPOSE: computes the right syzygy module of the module, generated by the rows of R, i.e. |
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94 | @* a matrix X with R*X=0 |
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95 | EXAMPLE: example rsyz; shows example |
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96 | " |
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97 | { |
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98 | def save = basering; // with respect to non-commutative rings, |
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99 | def saveop = opposite(save); // we have to switch to the oppose ring for a rightsyzygy |
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100 | setring saveop; |
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101 | matrix Rop = oppose(save,R); |
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102 | matrix Bop = syz(Rop); |
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103 | setring save; |
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104 | matrix B =oppose(saveop,Bop); |
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105 | kill saveop; |
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106 | return(B); |
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107 | } |
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108 | example |
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109 | {"EXAMPLE:";echo = 2; |
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110 | ring D = 0,(x,y,z),dp; |
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111 | matrix R[3][2]=x,0,0,x,y,-z; |
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112 | matrix X=rsyz(R); |
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113 | print(X); |
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114 | // check |
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115 | print(R*X); |
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116 | } |
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117 | |
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118 | |
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119 | static proc rinv (matrix R) |
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120 | "USAGE: rinv(R), R a matrix |
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121 | RETURN: matrix, a right inverse of R |
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122 | PURPOSE: computes a right inverse matrix of R, if it exists |
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123 | @* if not, it returns the zero matrix |
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124 | " |
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125 | { |
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126 | return(rightInverse(R)); |
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127 | } |
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128 | |
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129 | static proc linv (matrix R) |
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130 | "USAGE: linv(R), R a matrix |
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131 | RETURN: matrix, a left inverse of R |
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132 | PURPOSE: computes a left inverse matrix of R, if it exists |
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133 | @* if not, it returns the zero matrix |
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134 | " |
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135 | { |
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136 | return (leftInverse(R)); |
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137 | } |
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138 | |
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139 | proc rlift(matrix M, matrix N) |
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140 | "USAGE: rlift(M,N), M and N matrices, so that the module, generated by the columns of N |
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141 | @* is a submodule of the one, generated by the columns of M |
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142 | RETURN: matrix, a right lift of N in M |
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143 | PURPOSE: computes a right lift matrix X of N in M, |
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144 | @* i.e. N=M*X |
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145 | " |
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146 | { |
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147 | def save = basering; // with respect to non-commutative rings, |
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148 | def saveop = opposite(save); // we have to change the ring for a rightlift |
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149 | setring saveop; |
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150 | matrix Mop = oppose(save,M); |
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151 | matrix Nop = oppose(save,N); |
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152 | matrix Bop = lift(Mop,Nop); |
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153 | setring save; |
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154 | matrix B =oppose(saveop,Bop); |
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155 | kill saveop; |
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156 | return(B); |
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157 | } |
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158 | |
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159 | proc llift(matrix M, matrix N) |
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160 | "USAGE: llift(M,N), M and N matrices, so that the module, generated by the rows of N |
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161 | @* is a submodule of the one, generated by the rows of M |
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162 | RETURN: matrix, a left lift of N in M |
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163 | PURPOSE: computes a left lift matrix X of N in M, |
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164 | @* i.e. N=X*M |
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165 | " |
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166 | { |
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167 | matrix X=transpose(lift(transpose(M),transpose(N))); |
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168 | return(X); |
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169 | } |
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170 | |
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171 | static proc concatz(matrix M, matrix N) |
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172 | "USAGE: concatz(M,N), M and N matrices |
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173 | RETURN: matrix |
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174 | PURPOSE: adds the rows of N under the rows of M, i.e. build the matrix (M^Tr,N^Tr)^Tr |
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175 | " |
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176 | { |
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177 | matrix X=transpose(concat(transpose(M),transpose(N))); |
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178 | return (X); |
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179 | } |
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180 | |
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181 | //------------------------- main procedures -------------------------- |
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182 | |
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183 | proc purityFiltration(matrix R) |
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184 | "USAGE: purityFiltration(S), S matrix with entries of an Auslander regular ring D |
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185 | RETURN: a list T of two lists, purity filtration of the module M=D^q/D^p(S^t) |
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186 | PURPOSE: the first list T[1] gives a filtration {M_i} of M, |
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187 | @* where the i-th entry of T[1] gives the representation matrix of M_(i-1). |
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188 | @* the second list T[2] gives representations of the factor Modules, |
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189 | @* i.e. T[2][i] gives the repr. matrix for M_(i-1)/M_i |
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190 | EXAMPLE: example purityFiltration; shows example |
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191 | " |
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192 | { |
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193 | int i,j; |
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194 | list re=projectiveDimension(R,0); |
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195 | list T=re[1]; |
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196 | int di=re[2]; |
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197 | list reres; // Rji=reres[i][j+1], i=1,..,n+1; j=0,..,i |
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198 | for( i=1; i<=di+1; i++ ) |
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199 | { |
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200 | list zw; |
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201 | zw[i+1]=T[i]; |
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202 | for( j=i; j >= 1; j--) |
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203 | { |
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204 | zw[j]=rsyz(zw[j+1]); |
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205 | } |
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206 | reres[i]=zw; |
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207 | kill zw; |
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208 | } |
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209 | list F; // Fij=F[j][i+1], j=2,..,n+1; i=0,..,j-1 |
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210 | for(i=2;i<=di;i++) |
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211 | { |
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212 | list ehm; |
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213 | matrix I[nrows(T[i-1])][nrows(T[i-1])]; |
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214 | I=I+1; |
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215 | ehm[i]=I; |
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216 | kill I; |
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217 | for (j=1; j<=i-1; j++) |
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218 | { |
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219 | ehm[i-j]=rlift(reres[i][i-j+1],ehm[i-j+1]*reres[i-1][i-j+1]); |
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220 | } |
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221 | F[i]=ehm; |
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222 | kill ehm; |
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223 | } |
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224 | // list M; // Mi=M[i+1], i=0,...,n+1 |
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225 | // M[1]=R1; |
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226 | // matrix Ti=lsyz(reres[1][1]); |
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227 | // matrix P[ncols(Ti)][ncols(Ti)]; |
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228 | // P=P+1; |
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229 | // for (i=1;i<=di; i++) |
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230 | // { |
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231 | // M[i+1]=transpose(modulo(transpose(Ti*P),transpose(reres[i][2]))); |
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232 | // P=F[i+1][1]*P; |
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233 | // Ti=lsyz(reres[i+1][1]); |
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234 | // } |
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235 | // M[di+2]=transpose(modulo(transpose(Ti*P),transpose(reres[di+1][2]))); |
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236 | // list I; |
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237 | // for (i=1;i<=di+1;i++) |
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238 | // { |
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239 | // I[i]=transpose(modulo(transpose(M[i]),transpose(M[i+1]))); |
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240 | // } |
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241 | list Rs,Rss; |
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242 | for(i=1; i<=di; i++) |
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243 | { |
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244 | list zw; |
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245 | zw[1]=lsyz(reres[i][1]); |
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246 | zw[2]=lsyz(zw[1]); |
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247 | Rss[i]=llift(zw[1],reres[i][2]); |
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248 | Rs[i]=zw; |
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249 | kill zw; |
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250 | } |
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251 | list Fs; |
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252 | for(i=2;i<=di;i++) |
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253 | { |
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254 | Fs[i]=llift(Rs[i-1][1],Rs[i][1]*F[i][1]); |
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255 | } |
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256 | list K,U; |
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257 | K[1]=transpose(R); |
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258 | U[1]=Rs[1][1]; |
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259 | for(i=2;i<=di;i++) |
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260 | { |
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261 | K[i]=transpose(std(transpose(concatz(Rss[i-1], Rs[i-1][2])))); |
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262 | U[i]=transpose(std(transpose(concatz(concatz(Fs[i],Rss[i-1]),Rs[i-1][2])))); |
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263 | } |
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264 | K[di+1]=transpose(std(transpose(concatz(Rss[di], Rs[di][2])))); |
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265 | U[di+1]=K[di+1]; |
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266 | list erg=(K,U); |
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267 | return (erg); |
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268 | } |
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269 | example |
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270 | {"EXAMPLE:";echo = 2; |
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271 | ring D = 0,(x1,x2,d1,d2),dp; |
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272 | def S=Weyl(); |
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273 | setring S; |
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274 | int i; |
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275 | matrix R[3][3]=0,d2-d1,d2-d1,d2,-d1,-d1-d2,d1,-d1,-2*d1; |
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276 | print(R); |
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277 | list T=purityFiltration(transpose(R)); |
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278 | // the purity filtration of coker(M) |
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279 | print(T[1][1]); |
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280 | print(T[1][2]); |
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281 | print(T[1][3]); |
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282 | // factor modules of the filtration |
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283 | print(T[2][1]); |
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284 | print(T[2][2]); |
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285 | print(T[2][3]); |
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286 | } |
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287 | |
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288 | |
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289 | proc purityTriang(matrix R) |
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290 | "USAGE: purityTriang(S), S matrix with entries of an Auslander regular ring D |
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291 | RETURN: a matrix T |
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292 | PURPOSE: compute a triangular block matrix T, such that M=D^p/D^q(S^t) is isomorphic to M'=D^p'/D^q(T^t) |
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293 | EXAMPLE: example purityTriang; shows example |
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294 | " |
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295 | { |
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296 | int i,j; |
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297 | list re=projectiveDimension(R,0); |
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298 | list T=re[1]; |
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299 | int di=re[2]; |
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300 | list reres; // Rji=reres[i][j+1], i=1,..,n+1; j=0,..,i |
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301 | for( i=1; i<=di+1; i++ ) |
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302 | { |
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303 | list zw; |
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304 | zw[i+1]=T[i]; |
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305 | for( j=i; j >= 1; j--) |
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306 | { |
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307 | zw[j]=rsyz(zw[j+1]); |
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308 | } |
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309 | reres[i]=zw; |
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310 | kill zw; |
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311 | } |
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312 | list F; // Fij=F[j][i+1], j=2,..,n+1; i=0,..,j-1 |
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313 | for(i=2;i<=di;i++) |
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314 | { |
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315 | list ehm; |
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316 | matrix I[nrows(T[i-1])][nrows(T[i-1])]; |
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317 | I=I+1; |
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318 | ehm[i]=I; |
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319 | kill I; |
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320 | for (j=1; j<=i-1; j++) |
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321 | { |
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322 | ehm[i-j]=rlift(reres[i][i-j+1],ehm[i-j+1]*reres[i-1][i-j+1]); |
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323 | } |
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324 | F[i]=ehm; |
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325 | kill ehm; |
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326 | } |
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327 | |
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328 | list Rs,Rss; |
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329 | for(i=1; i<=di; i++) |
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330 | { |
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331 | list zw; |
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332 | zw[1]=lsyz(reres[i][1]); |
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333 | zw[2]=lsyz(zw[1]); |
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334 | Rss[i]=llift(zw[1],reres[i][2]); |
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335 | Rs[i]=zw; |
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336 | kill zw; |
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337 | } |
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338 | list Fs; |
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339 | for(i=2;i<=di;i++) |
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340 | { |
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341 | Fs[i]=llift(Rs[i-1][1],Rs[i][1]*F[i][1]); |
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342 | } |
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343 | |
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344 | |
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345 | int sp; list spnr; |
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346 | spnr[1]=ncols(Rs[1][1]); |
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347 | for (i=2;i<=di;i++) |
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348 | { |
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349 | spnr[i]=ncols(Fs[i]); |
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350 | } |
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351 | spnr[di+1]=ncols(Rss[di]); |
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352 | sp=sum(spnr); |
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353 | |
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354 | matrix E[nrows(Rs[1][1])][nrows(Rs[1][1])]; E=E-1; |
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355 | list Z; int sumh; |
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356 | Z[1]=concat(Rs[1][1],E); |
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357 | sumh=ncols(Rs[1][1]); |
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358 | kill E; |
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359 | |
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360 | for(i=2;i<=di;i++) |
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361 | { |
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362 | matrix A; |
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363 | matrix B[1][sumh]; |
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364 | matrix E[nrows(Fs[i])][nrows(Fs[i])]; E=E-1; |
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365 | |
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366 | A=Fs[i]; |
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367 | if (i>2) |
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368 | { |
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369 | if (iszero(Rss[i-1])==0) |
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370 | { |
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371 | A=concatz(A,Rss[i-1]); |
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372 | } |
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373 | } |
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374 | if (iszero(Rs[i-1][2])==0) |
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375 | { |
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376 | A=concatz(A,Rs[i-1][2]); |
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377 | } |
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378 | A=concat(B,A,E); |
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379 | Z[i]=A; |
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380 | sumh=sumh+spnr[i]; |
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381 | kill A,B,E; |
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382 | } |
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383 | |
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384 | |
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385 | matrix hi,his; |
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386 | matrix N[1][sumh]; |
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387 | |
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388 | if (iszero(Rss[di])==0) |
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389 | { |
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390 | hi=concat(N,Rss[di]); |
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391 | } |
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392 | |
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393 | if (iszero(Rs[di][2])==0) |
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394 | { |
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395 | his=concat(N,Rs[di][2]); |
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396 | if (iszero(hi)==1) |
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397 | { |
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398 | hi=his; |
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399 | } |
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400 | if (iszero(hi)==0) |
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401 | { |
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402 | hi=concatz(hi,his); |
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403 | } |
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404 | } |
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405 | |
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406 | kill his; |
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407 | |
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408 | matrix ges=Z[1]; |
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409 | for (i=2;i<=di;i++) |
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410 | { |
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411 | ges = concatz(ges,Z[i]); |
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412 | } |
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413 | |
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414 | if (iszero(hi)==0) |
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415 | { |
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416 | ges=concatz(ges,hi); |
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417 | } |
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418 | return (ges); |
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419 | } |
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420 | example |
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421 | {"EXAMPLE:";echo = 2; |
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422 | ring D = 0,(x1,x2,d1,d2),dp; |
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423 | def S=Weyl(); |
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424 | setring S; |
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425 | int i; |
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426 | matrix R[3][3]=0,d2-d1,d2-d1,d2,-d1,-d1-d2,d1,-d1,-2*d1; |
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427 | print(R); |
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428 | matrix T=purityTriang(transpose(R)); |
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429 | // a triangular blockmatrix representing the module coker(R) |
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430 | print(T); |
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431 | } |
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432 | |
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433 | |
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434 | proc gradeNumber(matrix R) |
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435 | "USAGE: gradeNumber(R), R matrix, representing M=D^p/D^q(R^t) over a ring D |
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436 | RETURN: int, grade number of M |
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437 | PURPOSE: computes the grade number of M, i.e. the first i, with ext^i(M,D) !=0 |
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438 | @* returns -1 if M=0 |
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439 | EXAMPLE: example gradeNumber; shows examples |
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440 | " |
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441 | { |
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442 | matrix M=transpose(R); |
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443 | if (is_zero(transpose(M))==1) |
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444 | { |
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445 | return (-1); |
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446 | } |
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447 | list ext = allExtOfLeft(transpose(M)); |
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448 | int i=1; |
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449 | matrix L=ext[i]; |
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450 | while (is_zero(transpose(L))==1) |
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451 | { |
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452 | i=i+1; |
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453 | L=ext[i]; |
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454 | } |
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455 | return (i-1); |
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456 | } |
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457 | example |
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458 | {"EXAMPLE:";echo = 2; |
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459 | // trivial example |
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460 | ring D=0,(x,y,z),dp; |
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461 | matrix R[2][1]=1,x; |
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462 | gradeNumber(R); |
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463 | // R has left inverse, so M=D/D^2R=0 |
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464 | gradeNumber(transpose(R)); |
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465 | print(ncExt_R(0,R)); |
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466 | // so, ext^0(coker(R),D) =! 0) |
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467 | // |
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468 | // a little bit more complex |
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469 | matrix R1[3][1]=x,-y,z; |
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470 | gradeNumber(transpose(R1)); |
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471 | print(ncExt_R(0,transpose(R1))); |
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472 | print(ncExt_R(1,transpose(R1))); |
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473 | print(ncExt_R(2,transpose(R1))); |
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474 | // ext^i are zero for i=0,1,2 |
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475 | matrix ext3=ncExt_R(3,transpose(R1)); |
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476 | print(ext3); |
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477 | // not zero |
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478 | is_zero(ext3); |
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479 | } |
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480 | |
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481 | proc allExtOfLeft(matrix Ps) |
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482 | "USAGE: allExtOfLeft(M), |
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483 | RETURN: list, entries are ext-modules |
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484 | ASSUME: M presents a left module of finite left projective dimension n |
---|
485 | PURPOSE: For a left module presented by M over the basering D, |
---|
486 | @* compute a list T, whose entry T[i+1] is a matrix, presenting the right module Ext^i_D(M,D) for i=0..n |
---|
487 | EXAMPLE: example allExtOfLeft; shows example |
---|
488 | " |
---|
489 | { |
---|
490 | // old doc: ... T[i] gives the repr. matrix of ext^(i-1)(M,D), i=1,.., n+1 |
---|
491 | list ext, Phi; |
---|
492 | ext[1]=ncHom_R(Ps); |
---|
493 | Phi = mres(Ps,0); |
---|
494 | int di = size(Phi); |
---|
495 | Phi[di+1]= transpose(lsyz(transpose(Phi[di]))); |
---|
496 | int i; |
---|
497 | def Rbase = basering; |
---|
498 | for(i=1;i<=di;i++) |
---|
499 | { |
---|
500 | module f = transpose(matrix(Phi[i+1])); |
---|
501 | module Im2 = transpose(matrix(Phi[i])); |
---|
502 | def Rop = opposite(Rbase); |
---|
503 | setring Rop; |
---|
504 | module fop = oppose(Rbase,f); |
---|
505 | module Im2op = oppose(Rbase,Im2); |
---|
506 | module ker_op = modulo(fop,std(0)); |
---|
507 | module ext_op = modulo(ker_op,Im2op); |
---|
508 | setring Rbase; |
---|
509 | ext[i+1] = oppose(Rop,ext_op); // a right module! |
---|
510 | kill f, Im2, Rop; |
---|
511 | } |
---|
512 | return(ext); |
---|
513 | } |
---|
514 | example |
---|
515 | {"EXAMPLE:";echo = 2; |
---|
516 | ring D = 0,(x,y,z),dp; |
---|
517 | matrix R[6][4]= |
---|
518 | 0,-2*x,z-2*y-x,-1, |
---|
519 | 0,z-2*x,2*y-3*x,1, |
---|
520 | z,-6*x,-2*y-5*x,-1, |
---|
521 | 0,y-x,y-x,0, |
---|
522 | y,-x,-y-x,0, |
---|
523 | x,-x,-2*x,0; |
---|
524 | // coker(R) consider the left module M=D^6/D^4R |
---|
525 | list T=allExtOfLeft(transpose(R)); |
---|
526 | print(T[1]); |
---|
527 | print(T[2]); |
---|
528 | print(T[3]); |
---|
529 | print(T[4]); |
---|
530 | // right modules coker(T[i].)!! |
---|
531 | } |
---|
532 | |
---|
533 | proc allExtOfRight(matrix Ps) |
---|
534 | "USAGE: allExtOfRight(R), R matrix representing the right Module M=D^q/RD^p over a ring D |
---|
535 | @* M module with finite right projective dimension n |
---|
536 | RETURN: list, entries are ext-modules |
---|
537 | PURPOSE: computes a list T, which entries are representations of the left modules ext^i(M,D) |
---|
538 | @* T[i] gives the repr. matrix of ext^(i-1)(M,D), i=1,..,n+1 |
---|
539 | EXAMPLE: example allExtOfRight; shows example |
---|
540 | " |
---|
541 | { |
---|
542 | // matrix Ps=transpose(Y); |
---|
543 | list ext, Phi; |
---|
544 | def Rbase = basering; |
---|
545 | def Rop = opposite(Rbase); |
---|
546 | setring Rop; |
---|
547 | matrix Psop=oppose(Rbase,Ps); |
---|
548 | matrix ext1_op = ncHom_R(Psop); |
---|
549 | setring Rbase; |
---|
550 | ext[1]=oppose(Rop,ext1_op); |
---|
551 | kill Rop; |
---|
552 | list zw = rightreso(transpose(Ps)); // right resolution |
---|
553 | int di = size(zw); |
---|
554 | zw[di+1]=lsyz(zw[di]); |
---|
555 | Phi = zw; |
---|
556 | kill zw; |
---|
557 | int i; |
---|
558 | for(i=1;i<=di;i++) |
---|
559 | { |
---|
560 | module f = Phi[i+1]; |
---|
561 | module Im2 = Phi[i]; |
---|
562 | module ker = modulo(f,std(0)); |
---|
563 | ext[i+1] = modulo(ker,Im2); // a left module! |
---|
564 | kill f, Im2, ker; |
---|
565 | } |
---|
566 | return(ext); |
---|
567 | } |
---|
568 | example |
---|
569 | {"EXAMPLE:";echo = 2; |
---|
570 | ring D = 0,(x,y,z),dp; |
---|
571 | matrix R[6][4]= |
---|
572 | 0,-2*x,z-2*y-x,-1, |
---|
573 | 0,z-2*x,2*y-3*x,1, |
---|
574 | z,-6*x,-2*y-5*x,-1, |
---|
575 | 0,y-x,y-x,0, |
---|
576 | y,-x,-y-x,0, |
---|
577 | x,-x,-2*x,0; |
---|
578 | // coker(R) considered as right module |
---|
579 | projectiveDimension(R,1)[2]; |
---|
580 | list T=allExtOfRight(R); |
---|
581 | print(T[1]); |
---|
582 | print(T[2]); |
---|
583 | // left modules coker(.T[i])!! |
---|
584 | } |
---|
585 | |
---|
586 | static proc rightreso(matrix T) |
---|
587 | "USAGE: rightreso(T), T matrix representing the right module M=D*/TD* |
---|
588 | RETURN: list L, a right resolution of M |
---|
589 | PURPOSE: computes a right resolution of M, using mres |
---|
590 | @* the i-th entry of L gives the (i-1)th right syzygy module of M |
---|
591 | " |
---|
592 | { |
---|
593 | int j; |
---|
594 | matrix M=transpose(T); |
---|
595 | list res; |
---|
596 | def save = basering; // with respect to non-commutative rings, |
---|
597 | def saveop = opposite(save); // we have to change the ring for a rightresolution |
---|
598 | setring saveop; |
---|
599 | matrix Mop=oppose(save,M); |
---|
600 | list aufl=mres(Mop,0); |
---|
601 | list resop=aufl; |
---|
602 | kill aufl; |
---|
603 | for (j=1; j<=size(resop); j++) |
---|
604 | { |
---|
605 | matrix zw=resop[j]; |
---|
606 | setring save; |
---|
607 | res[j]=transpose(oppose(saveop,zw)); |
---|
608 | setring saveop; |
---|
609 | kill zw; |
---|
610 | } |
---|
611 | setring save; |
---|
612 | kill saveop; |
---|
613 | return(res); |
---|
614 | } |
---|
615 | |
---|
616 | proc showgrades(list T) |
---|
617 | "USAGE: showgrades(T), T list, which includes representation matrices of modules |
---|
618 | RETURN: list, gradenumbers of the entries in T |
---|
619 | PURPOSE: computes a list L with L[i]=gradenumber(M), M=D^p/D^qT[i] |
---|
620 | EXAMPLE: example showgrades; shows example |
---|
621 | " |
---|
622 | { |
---|
623 | list grades; |
---|
624 | int gr=size(T); |
---|
625 | int i; |
---|
626 | for (i=1;i<=gr;i++) |
---|
627 | { |
---|
628 | grades[i]=gradeNumber(transpose(T[i])); |
---|
629 | } |
---|
630 | return (grades); |
---|
631 | } |
---|
632 | example |
---|
633 | {"EXAMPLE:";echo = 2; |
---|
634 | ring D = 0,(x,y,z),dp; |
---|
635 | matrix R[6][4]= |
---|
636 | 0,-2*x,z-2*y-x,-1, |
---|
637 | 0,z-2*x,2*y-3*x,1, |
---|
638 | z,-6*x,-2*y-5*x,-1, |
---|
639 | 0,y-x,y-x,0, |
---|
640 | y,-x,-y-x,0, |
---|
641 | x,-x,-2*x,0; |
---|
642 | list T=purityFiltration(transpose(R))[2]; |
---|
643 | showgrades(T); |
---|
644 | // T[i] are i-1 pure (i=1,3,4) or zero (i=2) |
---|
645 | } |
---|
646 | |
---|
647 | proc doubleExt(matrix R, int i) |
---|
648 | "USAGE: doubleExt(R,i), R matrix representing the left Module M=D^p/D^q(R^t) over a ring D |
---|
649 | @* int i, less or equal the left projective dimension of M |
---|
650 | RETURN: matrix P, representing the double ext module |
---|
651 | PURPOSE: computes a matrix P, which represents the left module ext^i(ext^i(M,D)) |
---|
652 | EXAMPLE: example doubleExt; shows example |
---|
653 | " |
---|
654 | { |
---|
655 | return (allExtOfRight( allExtOfLeft(R)[i+1] )[i+1]); |
---|
656 | } |
---|
657 | example |
---|
658 | {"EXAMPLE:";echo = 2; |
---|
659 | ring D = 0,(x,y,z),dp; |
---|
660 | matrix R[7][3]= |
---|
661 | 0 ,0,1, |
---|
662 | 1 ,-4*x+z,-z, |
---|
663 | -1,8*x-2*z,z, |
---|
664 | 1 ,0 ,0, |
---|
665 | 0 ,x-y,0, |
---|
666 | 0 ,x-y,y, |
---|
667 | 0 ,0 ,x; |
---|
668 | // coker(R) is 2-pure, so all doubleExt are zero |
---|
669 | print(doubleExt(transpose(R),0)); |
---|
670 | print(doubleExt(transpose(R),1)); |
---|
671 | print(doubleExt(transpose(R),3)); |
---|
672 | // except of the second |
---|
673 | print(doubleExt(transpose(R),2)); |
---|
674 | } |
---|
675 | |
---|
676 | proc allDoubleExt(matrix R) |
---|
677 | "USAGE: allDoubleExt(R), R matrix representing the left Module M=D^p/D^q(R^t) over a ring D |
---|
678 | RETURN: list T, double indexed, which include all double-ext modules |
---|
679 | PURPOSE: computes all double ext-modules |
---|
680 | @* T[i][j] gives a representation matrix of ext^(j-1)(ext(i-1)(M,D)) |
---|
681 | EXAMPLE: example allDoubleExt; shows example |
---|
682 | " |
---|
683 | { |
---|
684 | list ext=allExtOfLeft(transpose(R)); |
---|
685 | list extext; |
---|
686 | int i; |
---|
687 | for(i=1;i<=size(ext);i++) |
---|
688 | { |
---|
689 | extext[i]=allExtOfRight(ext[i]); |
---|
690 | } |
---|
691 | kill ext; |
---|
692 | return (extext); |
---|
693 | } |
---|
694 | example |
---|
695 | {"EXAMPLE:";echo = 2; |
---|
696 | ring D = 0,(x1,x2,x3,d1,d2,d3),dp; |
---|
697 | def S=Weyl(); |
---|
698 | setring S; |
---|
699 | matrix R[6][4]= |
---|
700 | 0,-2*d1,d3-2*d2-d1,-1, |
---|
701 | 0,d3-2*d1,2*d2-3*d1,1, |
---|
702 | d3,-6*d1,-2*d2-5*d1,-1, |
---|
703 | 0,d2-d1,d2-d1,0, |
---|
704 | d2,-d1,-d2-d1,0, |
---|
705 | d1,-d1,-2*d1,0; |
---|
706 | list T=allDoubleExt(transpose(R)); |
---|
707 | // left projective dimension of M=coker(R) is 3 |
---|
708 | // ext^i(ext^0(M,D)), i=0,1,2,3 |
---|
709 | print(T[1][1]); |
---|
710 | print(T[1][2]); |
---|
711 | print(T[1][3]); |
---|
712 | print(T[1][4]); |
---|
713 | // ext^i(ext^1(M,D)), i=0,1,2,3 |
---|
714 | print(T[2][1]); |
---|
715 | print(T[2][2]); |
---|
716 | print(T[2][3]); |
---|
717 | print(T[2][4]); |
---|
718 | // ext^i(ext^2(M,D)), i=0,1,2,3 (all zero) |
---|
719 | print(T[3][1]); |
---|
720 | print(T[3][2]); |
---|
721 | print(T[3][3]); |
---|
722 | print(T[3][4]); |
---|
723 | // ext^i(ext^3(M,D)), i=0,1,2,3 (all zero) |
---|
724 | print(T[4][1]); |
---|
725 | print(T[4][2]); |
---|
726 | print(T[4][3]); |
---|
727 | print(T[4][4]); |
---|
728 | } |
---|
729 | |
---|
730 | proc is_pure(matrix R) |
---|
731 | "USAGE: is_pure(R), R representing the module M=D^p/D^q(R^t) |
---|
732 | RETURN: int, 0 or 1 |
---|
733 | PURPOSE: checks pureness of M. |
---|
734 | @* returns 1, if M is pure, or 0, if it's not |
---|
735 | @* remark: if M is zero, is_pure returns 1 |
---|
736 | EXAMPLE: example is_pure; shows example |
---|
737 | " |
---|
738 | { |
---|
739 | matrix M=transpose(R); |
---|
740 | int gr=gradeNumber(transpose(M)); |
---|
741 | int di=projectiveDimension(transpose(M),0)[2]; |
---|
742 | int i=0; |
---|
743 | while(i<=di) |
---|
744 | { |
---|
745 | if (i!=gr) |
---|
746 | { |
---|
747 | if ( is_zero( doubleExt(transpose(M),i) ) == 0 ) |
---|
748 | { |
---|
749 | return (0); |
---|
750 | } |
---|
751 | } |
---|
752 | i=i+1; |
---|
753 | } |
---|
754 | return (1); |
---|
755 | } |
---|
756 | example |
---|
757 | {"EXAMPLE:";echo = 2; |
---|
758 | ring D = 0,(x,y,z),dp; |
---|
759 | matrix R[3][2]=y,-z,x,0,0,x; |
---|
760 | list T=purityFiltration(transpose(R)); |
---|
761 | print(transpose(std(transpose(T[2][2])))); |
---|
762 | // so the purity filtration of coker(R) is trivial, |
---|
763 | // i.e. coker(R) is already pure |
---|
764 | is_pure(transpose(R)); |
---|
765 | // we can also have non-pure modules: |
---|
766 | matrix R2[6][4]= |
---|
767 | 0,-2*x,z-2*y-x,-1, |
---|
768 | 0,z-2*x,2*y-3*x,1, |
---|
769 | z,-6*x,-2*y-5*x,-1, |
---|
770 | 0,y-x,y-x,0, |
---|
771 | y,-x,-y-x,0, |
---|
772 | x,-x,-2*x,0; |
---|
773 | is_pure(transpose(R2)); |
---|
774 | } |
---|
775 | |
---|
776 | proc purelist(list T) |
---|
777 | "USAGE: purelist(T), T list, in which the i-th entry R=T[i] represents M=D^p/D^q(R^t) |
---|
778 | RETURN: list M, entries of M are 0 or 1 |
---|
779 | PURPOSE: if T[i] is pure, M[i] is 1, else M[i] is 0 |
---|
780 | EXAMPLE: example purelist; shows example |
---|
781 | " |
---|
782 | { |
---|
783 | int i; |
---|
784 | list erg; |
---|
785 | for(i=1;i<=size(T);i++) |
---|
786 | { |
---|
787 | erg[i]=is_pure(transpose(T[i])); |
---|
788 | } |
---|
789 | return (erg); |
---|
790 | } |
---|
791 | example |
---|
792 | {"EXAMPLE:";echo = 2; |
---|
793 | ring D = 0,(x,y,z),dp; |
---|
794 | matrix R[6][4]= |
---|
795 | 0,-2*x,z-2*y-x,-1, |
---|
796 | 0,z-2*x,2*y-3*x,1, |
---|
797 | z,-6*x,-2*y-5*x,-1, |
---|
798 | 0,y-x,y-x,0, |
---|
799 | y,-x,-y-x,0, |
---|
800 | x,-x,-2*x,0; |
---|
801 | is_pure(transpose(R)); |
---|
802 | // R is not pure, so we do the purity filtration |
---|
803 | list T=purityFiltration(transpose(R)); |
---|
804 | // all Elements of T[2] are either zero or pure |
---|
805 | purelist(T[2]); |
---|
806 | } |
---|
807 | |
---|
808 | |
---|
809 | proc projectiveDimension(matrix T, list #) |
---|
810 | "USAGE: projectiveDimension(R,i,j), R matrix representing the Modul M=coker(R) |
---|
811 | @* int i, with i=0 or i=1, j a natural number |
---|
812 | RETURN: list T, a projective resolution of M and its projective dimension |
---|
813 | PURPOSE: if i=0 (and by default), T[1] gives a shortest left resolution of M=D^p/D^q(R^t) and T[2] the left projective dimension of M |
---|
814 | @* if i=1, T[1] gives a shortest right resolution of M=D^p/RD^q and T[2] the right projective dimension of M |
---|
815 | @* in both cases T[1][j] is the (j-1)-th syzygy module of M |
---|
816 | NOTE: The algorithm is due to A. Quadrat, D. Robertz, Computation of bases of free modules over the Weyl algebras, J.Symb.Comp. 42, 2007. |
---|
817 | EXAMPLE: example projectiveDimension; shows examples |
---|
818 | " |
---|
819 | { |
---|
820 | int i = 0; // default |
---|
821 | if (size(#) >0) |
---|
822 | { |
---|
823 | i = int(#[1]); |
---|
824 | if ( (i!=0) and (i!=1) ) |
---|
825 | { |
---|
826 | printf("Unaccepted second argument. Use 0 to get a left resolution, 1 for a right one."); |
---|
827 | } |
---|
828 | } |
---|
829 | if (i==0) |
---|
830 | { |
---|
831 | return(prodim(T)); |
---|
832 | } |
---|
833 | int j; |
---|
834 | matrix M=T; |
---|
835 | list res; |
---|
836 | def save = basering; // with respect to non-commutative rings, |
---|
837 | def saveop = opposite(save); // we have to change the ring for a rightresolution |
---|
838 | setring saveop; |
---|
839 | matrix Mop=oppose(save,M); |
---|
840 | list aufl=prodim(Mop); |
---|
841 | int k=aufl[2]; |
---|
842 | list resop=aufl[1]; |
---|
843 | kill aufl; |
---|
844 | for (j=1; j<=size(resop); j++) |
---|
845 | { |
---|
846 | matrix zw=resop[j]; |
---|
847 | setring save; |
---|
848 | res[j]=transpose(oppose(saveop,zw)); |
---|
849 | setring saveop; |
---|
850 | kill zw; |
---|
851 | } |
---|
852 | setring save; |
---|
853 | list Y; |
---|
854 | Y[1]=res; |
---|
855 | Y[2]=k; |
---|
856 | kill saveop; |
---|
857 | kill res; |
---|
858 | return(Y); |
---|
859 | |
---|
860 | } |
---|
861 | example |
---|
862 | {"EXAMPLE:";echo = 2; |
---|
863 | // commutative example |
---|
864 | ring D = 0,(x,y,z),dp; |
---|
865 | matrix R[6][4]= |
---|
866 | 0,-2*x,z-2*y-x,-1, |
---|
867 | 0,z-2*x,2*y-3*x,1, |
---|
868 | z,-6*x,-2*y-5*x,-1, |
---|
869 | 0,y-x,y-x,0, |
---|
870 | y,-x,-y-x,0, |
---|
871 | x,-x,-2*x,0; |
---|
872 | // compute a left resolution of M=D^4/D^6*R |
---|
873 | list T=projectiveDimension(transpose(R),0); |
---|
874 | // so we have the left projective dimension |
---|
875 | T[2]; |
---|
876 | //we could also compute a right resolution of M=D^6/RD^4 |
---|
877 | list T1=projectiveDimension(R,1); |
---|
878 | // and we have right projective dimension |
---|
879 | T1[2]; |
---|
880 | // check, that a syzygy matrix of R has left inverse: |
---|
881 | print(leftInverse(syz(R))); |
---|
882 | // so lpd(M) must be 1. |
---|
883 | // Non-commutative example |
---|
884 | ring D1 = 0,(x1,x2,x3,d1,d2,d3),dp; |
---|
885 | def S=Weyl(); setring S; |
---|
886 | matrix R[3][3]= |
---|
887 | 1/2*x2*d1, x2*d2+1, x2*d3+1/2*d1, |
---|
888 | -1/2*x2*d2-3/2,0,1/2*d2, |
---|
889 | -d1-1/2*x2*d3,-d2,-1/2*d3; |
---|
890 | list T=projectiveDimension(R,0); |
---|
891 | // left projective dimension of coker(R) is |
---|
892 | T[2]; |
---|
893 | list T1=projectiveDimension(R,1); |
---|
894 | // both modules have the same projective dimension, but different resolutions, because D is non-commutative |
---|
895 | print(T[1][1]); |
---|
896 | // not the same as |
---|
897 | print(transpose(T1[1][1])); |
---|
898 | } |
---|
899 | |
---|
900 | static proc prodim(matrix M) |
---|
901 | "USAGE: prodim(R), R matrix representing the Modul M=coker(R) |
---|
902 | RETURN: list T, a left projective resolution of M and its left projective dimension |
---|
903 | PURPOSE: T[1] gives a shortest left resolution of M and T[2] the left projective dimension of M |
---|
904 | @* it is T[1][j] the (j-1)-th syzygy module of M |
---|
905 | " |
---|
906 | { |
---|
907 | matrix T=transpose(M); |
---|
908 | list R,zw; |
---|
909 | R[1]=T; |
---|
910 | if (rinv(R[1])==0) |
---|
911 | { |
---|
912 | R[2]=transpose(std(transpose(lsyz(R[1])))); |
---|
913 | } |
---|
914 | else |
---|
915 | { |
---|
916 | matrix S[1][ncols(T)]; |
---|
917 | R[1]=S; |
---|
918 | zw[1]=R; |
---|
919 | zw[2]=0; |
---|
920 | return (zw); |
---|
921 | } |
---|
922 | if (iszero(R[2])==1) |
---|
923 | { |
---|
924 | zw[1]=R; |
---|
925 | zw[2]=1; |
---|
926 | return (zw); |
---|
927 | } |
---|
928 | int i=1; |
---|
929 | matrix N; |
---|
930 | while (iszero(R[i+1])==0) |
---|
931 | { |
---|
932 | i=i+1; |
---|
933 | N=rinv(R[i]); |
---|
934 | if (iszero(N)==0) |
---|
935 | { |
---|
936 | if (i==2) |
---|
937 | { |
---|
938 | R[i-1]=concat(R[i-1],N); |
---|
939 | matrix K[1][nrows(R[1])]; |
---|
940 | R[2]=K; |
---|
941 | zw[1]=R; |
---|
942 | zw[2]=i-1; |
---|
943 | return (zw); |
---|
944 | } |
---|
945 | if (i>2) |
---|
946 | { |
---|
947 | R[i-1]=concat(R[i-1],N); |
---|
948 | matrix K[ncols(N)][1]; |
---|
949 | R[i-2]=concatz(R[i-2],K); |
---|
950 | R[i]=0; |
---|
951 | zw[1]=R; |
---|
952 | zw[2]=i-1; |
---|
953 | return(zw); |
---|
954 | } |
---|
955 | } |
---|
956 | R[i+1]=transpose(std(transpose(lsyz(R[i])))); |
---|
957 | } |
---|
958 | zw[1]=R; |
---|
959 | zw[2]=i; |
---|
960 | return (zw); |
---|
961 | } |
---|