isModular -- determines if a lattice is modular

Synopsis

Usage:

i = isModular P
Inputs:
- P, an instance of the type Poset, a ranked lattice
Outputs:
- i, a Boolean value, whether $P$ is modular

Description

Let $r$ be the ranking of $P$. Then $P$ is modular if for every pair of vertices $a$ and $b$, $r(a) + r(b) = r(join(a,b)) + r(meet(a,b,))$. That is, $P$ is modular if it isLowerSemimodular and isUpperSemimodular.

The $n$ chain and the $n$ booleanLattice are modular.

i1 : n = 4;

i2 : isModular chain n

o2 = true

i3 : isModular booleanLattice n

o3 = true

The following lattice is not modular.

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 : isModular P

o6 = false

This method uses the methods isLowerSemimodular and isUpperSemimodular, which were ported from John Stembridge's Maple package available at http://www.math.lsa.umich.edu/~jrs/maple.html#posets.

Ways to use isModular :

isModular(Poset)

For the programmer

The object isModular is a method function.

isModular -- determines if a lattice is modular

Synopsis

Description

See also

Ways to use isModular :

For the programmer