Geometry of numbers

Source: Wikipedia, the free encyclopedia.

Geometry of numbers is the part of

ring of algebraic integers is viewed as a lattice
in and the study of these lattices provides fundamental information on algebraic numbers.[1] The geometry of numbers was initiated by Hermann Minkowski (1910).

Best rational approximants for π (green circle), e (blue diamond), ϕ (pink oblong), (√3)/2 (grey hexagon), 1/√2 (red octagon) and 1/√3 (orange triangle) calculated from their continued fraction expansions, plotted as slopes y/x with errors from their true values (black dashes)  

The geometry of numbers has a close relationship with other fields of mathematics, especially functional analysis and Diophantine approximation, the problem of finding rational numbers that approximate an irrational quantity.[2]

Minkowski's results

Suppose that is a lattice in -dimensional Euclidean space and is a convex centrally symmetric body. Minkowski's theorem, sometimes called Minkowski's first theorem, states that if , then contains a nonzero vector in .

The successive minimum is defined to be the

inf
of the numbers such that contains linearly independent vectors of . Minkowski's theorem on
successive minima, sometimes called Minkowski's second theorem, is a strengthening of his first theorem and states that[3]

Later research in the geometry of numbers

In 1930–1960 research on the geometry of numbers was conducted by many

Louis Mordell, Harold Davenport and Carl Ludwig Siegel). In recent years, Lenstra, Brion, and Barvinok have developed combinatorial theories that enumerate the lattice points in some convex bodies.[4]

Subspace theorem of W. M. Schmidt

In the geometry of numbers, the

forms in n variables with algebraic
coefficients and if ε>0 is any given real number, then the non-zero integer points x in n coordinates with

lie in a finite number of proper subspaces of Qn.

Influence on functional analysis

Minkowski's geometry of numbers had a profound influence on

Kolmogorov, whose theorem states that the symmetric convex sets that are closed and bounded generate the topology of a Banach space.[6]

Researchers continue to study generalizations to

References

  1. ^ MSC classification, 2010, available at http://www.ams.org/msc/msc2010.html, Classification 11HXX.
  2. ^ Cassels (1971) p. 203
  3. ^ Grötschel et al., Lovász et al., Lovász, and Beck and Robins.
  4. ^ Schmidt, Wolfgang M. Norm form equations. Ann. Math. (2) 96 (1972), pp. 526–551. See also Schmidt's books; compare Bombieri and Vaaler and also Bombieri and Gubler.
  5. ^ For Kolmogorov's normability theorem, see Walter Rudin's Functional Analysis. For more results, see Schneider, and Thompson and see Kalton et al.
  6. ^ Kalton et al. Gardner

Bibliography