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Posets :: isLowerSemimodular

isLowerSemimodular -- determines if a ranked lattice is lower semimodular

Synopsis

Description

Let r be the ranking of P. Then P is lower semimodular if for every pair of vertices a and b, r(a) + r(b) ≤r(join(a,b)) + r(meet(a,b,)).

The n chain and the n booleanLattice are lower semimodular.
i1 : n = 4;
i2 : isLowerSemimodular chain n

o2 = true
i3 : isLowerSemimodular booleanLattice n

o3 = true
The following lattice is not lower semimodular.
i4 : P = poset {{1, 2}, {1, 5}, {2, 3}, {2, 4}, {3, 7}, {4, 7}, {5, 4}, {5, 6}, {6, 7}};
i5 : isLattice P

o5 = true
i6 : isLowerSemimodular P

o6 = false
This method was ported from John Stembridge’s Maple package available at http://www.math.lsa.umich.edu/~jrs/maple.html#posets.

See also

Ways to use isLowerSemimodular :