# Diophantine Approximations

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## Diophantine Approximations

a part of the theory of numbers that studies approximations of real numbers by rational numbers or, in a broader context, problems involved in finding integral solutions of linear and nonlinear inequalities or systems of inequalities with real coefficients. Diophantine approximations are named after the ancient Greek mathematician Diophantus, who worked on the problem of finding integral solutions of algebraic equations (Diophantine equations). The methods of the theory of Diophantine approximations are based on the application of continued fractions, Farey sequences, and the Dirichlet principle.

The problem of approximating a number by rational fractions is solved with the aid of all three of these methods and particularly with the use of continued fractions. The approximation of a real number α by convergents pk/qk of the expansion of α into a continued fraction is characterized by the inequality │ αpk/qk │ < 1/qk2. On the other hand, if an irreducible fraction a/b satisfies the inequality │ α − a/b │ < 1/2b2, then it is a convergent in the expansion of α into a continued fraction. Fundamental work on the approximation of real numbers α by rational fractions has been done by A. A. Markov (Senior). There are many extensions of the problem of approximating a number by rational fractions. Among them, the primary problem is that of studying expressions of the type xθ − y − α, where θ and α are certain real numbers and x and y assume integral values (the so-called nonhomogeneous one-dimensional problem). The first results in solving this problem were achieved by P. L. Chebyshev. A well-known theorem on approximate integral solutions of systems of linear equations (multidimensional problems of Diophantine approximations), is the following theorem of L. Kronecker: If α1, …, αn are real numbers for which the equality a1α1 + … + anαn = 0 with integral a1, …, an holds only for a1 = … = an = 0 and β1, …, βn are certain real numbers, then for any ε > 0 it is possible to find a number t and also integers x1 …, xn, such that the inequalities │ t αk − βk − xk │ < ε for k = 1, 2, … , n. Dirichlet’ s principle is very useful in solving multidimensional problems of Diophantine approximations. Methods based on Dirichlet’s principle enabled A. Ia. Khinchin and other mathematicians to develop a systematic theory of multidimensional Diophantine approximations. An important aspect of the theory of Diophantine approximations is its connection with geometry based on the fact that a system of linear forms with real coefficients can be represented as a lattice in an n-dimensional arithmetic space. In the late 19th century H. Minkowski proved a number of geometric theorems applicable to the theory of Diophantine approximations.

I. M. Vinogradov obtained remarkable results in problems of nonlinear Diophantine approximations. The methods devised by him occupy a central position in this area of number theory. One of the most important problems of the theory of Diophantine approximations is that of approximating algebraic numbers by rational numbers.

The theory of transcendental numbers, in which estimates are found for norms of linear forms and polynomials in one and several numbers with integral coefficients, is related to Diophantine approximations. The theory of Diophantine approximations is closely related to the solution of Diophantine equations and to various problems of analytic number theory.

### REFERENCES

Vinogradov, I. M. Metod trigonometricheskikh summ v teorii chisel. Moscow, 1971.
Gel’fond, A. O. “Priblizhenie algebraicheskikh chisel algebraicheskimi zhe chislami i teoriia transtsendentnykh chisel.” Uspekhi matematicheskikh nauk, 1949, vol. 4, issue 4.
Fel’dman, N. I., and A. B. Shidlovskii. “Razvitie i sovremennoe sostoianie teorii transtsendentnykh chisel.” Uspekhi matematicheskikh nauk, 1967, vol. 22, issue 3.
Khinchin, A. Ia. Tsepnye drobi, 3rd ed. Moscow, 1961.
Koksma, J. F. Diophantische Approximationen. Berlin, 1936.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
1, 1 41], in On some applications of Diophantine approximations, Quad./Monogr., 2, Ed.
That content includes divisibility in the natural numbers, linear equations through the ages, the prime numbers, thinking cyclically, Fermat and Euler, cryptography, polynomial congruence, quadratic reciprocity, Pythagorean triples, sums of squares, Fermat's last theorem, diophantine approximations and Pell equations, primality testing, and mathematical induction.
Diophantine approximations. Let K be an algebraic number field of degree d.
Vojta, Diophantine Approximations and Value Distribution Theory, Lecture Notes in Math., vol.
The counterpart of the second main theorem in the Diophantine approximation is the Schmidt's subspace theorem.

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