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University of Paderborn Department of Mathematics Diploma Thesis ...

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4.4. COMPUTING EXPANSIONS AND CONTRACTIONS 95if m[i] > 0 thenmon:= m;mon[i]:= mon[i] - 1;mon[i+1]:= mon[i+1] + 1;RightShift:= RightShift union {mon};for j from i+1 to last doif m[j] = 0 thenmon:= m;mon[i]:= mon[i] - 1;mon[j+1]:= mon[j+1] + 1;RightShift:= RightShift union {mon};elsebreak;end_if;end_for;end_if;end_for;/* If any element <strong>of</strong> the right-shift is contained inthe set <strong>of</strong> minimal generators M <strong>of</strong> the idealconsidered, return FALSE (i.e. the monomial is notexpandable), otherwise return TRUE (i.e. the monomialis expandable). */for i from 1 to nops(RightShift) doif contains(M, RightShift[i]) > 0 thenreturn(FALSE);end_if;end_for;return(TRUE);end_proc:MuPAD Source Code 4.14. With the same notation as in 4.13, the following procedurechecks whether the monomial m is contractible in the ideal generated by the set M. Itreturns “TRUE” if m is contractible and “FALSE” if this is not the case.Input for the procedure test contractible.◦ M — a list <strong>of</strong> lists encoding the set <strong>of</strong> generators <strong>of</strong> some stable ideal in lexicographicorder◦ m — a list encoding a monomial◦ n — the index <strong>of</strong> the last variable <strong>of</strong> the polynomial ring R

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