Dirichlet approximation theorem

E637303

The Dirichlet approximation theorem is a fundamental result in Diophantine approximation that guarantees, for any real number and positive integer, the existence of a nearby rational number with bounded denominator and small approximation error.

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Predicate Object
instanceOf mathematical theorem
result in Diophantine approximation
appearsIn advanced undergraduate number theory courses
graduate courses on analytic number theory
introductory texts on Diophantine approximation
category theorem in analytic number theory
concerns approximation of real numbers by rationals
bounds on denominators of approximating fractions
coreConcept Diophantine inequality
fractional parts of multiples of a real number
lattice points in the plane
ensures existence of p and q with small |qα − p|
equivalentFormulation For any real α and positive integer N, there exist integers p and q with 1 ≤ q ≤ N such that |qα − p| < 1/N.
errorBound approximation error less than 1/(qN)
approximation error less than 1/q² for infinitely many rationals
field Diophantine approximation
number theory
generalizationOf basic rational approximation results from continued fractions
guarantees existence of good rational approximations to real numbers
hasVersion inhomogeneous approximation form
simultaneous approximation for vectors in R^n
historicalPeriod 19th century mathematics
holdsFor every positive integer N
every real number
implies existence of infinitely many good rational approximations to any irrational number
for any real α there are infinitely many rationals p/q with |α − p/q| < 1/q²
influenced development of modern Diophantine approximation theory
namedAfter Johann Peter Gustav Lejeune Dirichlet
prerequisiteFor Dirichlet's theorem on Diophantine approximation on manifolds (in basic form)
provides quantitative bound on rational approximation error
relatedTo Hurwitz's theorem
linked to: Hurwitz theorem

Kronecker approximation theorem
Minkowski's theorem in geometry of numbers
Roth's theorem
linked to: Roth theorem
statement For any real number α and any positive integer N, there exist integers p and q with 1 ≤ q ≤ N such that |α − p/q| < 1/(qN).
strength gives optimal exponent 2 in |α − p/q| < C/q² for general real numbers
usedIn geometry of numbers
metric Diophantine approximation
study of continued fractions
uniform distribution theory
usesMethod pigeonhole principle

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Referenced by (4)

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Diophantine approximation hasKeyResult Dirichlet approximation theorem
Dirichlet approximation theorem prerequisiteFor Dirichlet's theorem on Diophantine approximation on manifolds (in basic form)
linked to: Dirichlet approximation theorem
Hurwitz theorem refines Dirichlet approximation theorem
Roth's theorem comparesWith Dirichlet's approximation theorem
subject linked to: Roth theorem
linked to: Dirichlet approximation theorem