In the mathematical study of order, a metric lattice L is a lattice that admits a positive valuation: a function v ∈ L → ℝ satisfying, for any a, b ∈ L, v ( a ) + v ( b ) = v ( a ∧ b ) + v ( a ∨ b ) {\displaystyle v(a)+v(b)=v(a\wedge b)+v(a\vee b)} and a > b ⇒ v ( a ) > v ( b ) . {\displaystyle {a>b}\Rightarrow v(a)>v(b){\text{.}}}
Relation to other notions
A Boolean algebra is a metric lattice; any finitely-additive measure on its Stone dual gives a valuation. Every metric lattice is a modular lattice, c.f. lower picture. It is also a metric space, with distance function given by d ( x , y ) = v ( x ∨ y ) − v ( x ∧ y ) . {\displaystyle d(x,y)=v(x\vee y)-v(x\wedge y){\text{.}}} With that metric, the join and meet are uniformly continuous contractions, and so extend to the metric completion (metric space). That lattice is usually not the Dedekind-MacNeille completion, but it is conditionally complete.
Applications In the study of fuzzy logic and interval arithmetic, the space of uniform distributions is a metric lattice. Metric lattices are also key to von Neumann's construction of the continuous projective geometry. A function satisfies the one-dimensional wave equation if and only if it is a valuation for the lattice of spacetime coordinates with the natural partial order. A similar result should apply to any partial differential equation solvable by the method of characteristics, but key features of the theory are lacking.
References



