University of Paderborn Department of Mathematics Diploma Thesis ...

4.4. COMPUTING EXPANSIONS AND CONTRACTIONS 97mon:= m;mon[i]:= mon[i] - 1;mon[i-1]:= mon[i-1] + 1;LeftShift:= LeftShift union {mon};for j from i-1 downto 2 doif m[j] = 0 thenmon:= m;mon[i]:= mon[i] - 1;mon[j-1]:= mon[j-1] + 1;LeftShift:= LeftShift union {mon};elsebreak;end_if;end_for;end_if;end_for;/* Since the set M is ordered with respect to thelexicographic order, it suffices to check, whetherall elements of LeftShift are divisible by one ofthe monomials to the left of m.By ’pos’ we denote the position of this monomial(see above). */contractible:= FALSE;cnt:= nops(LeftShift);for i from 1 to nops(LeftShift) domon1:= LeftShift[i];for j from pos downto 1 domon2:= M[j];for k from n+1 downto 1 doif mon1[k] - mon2[k] >= 0 thencontractible:= TRUE;elsecontractible:= FALSE;break;end_if;end_for;if contractible = TRUE thencnt:= cnt - 1;break;end_if;