Hilbert's inequality
Encyclopedia
In complex analysis
Complex analysis
Complex analysis, traditionally known as the theory of functions of a complex variable, is the branch of mathematical analysis that investigates functions of complex numbers. It is useful in many branches of mathematics, including number theory and applied mathematics; as well as in physics,...

, a branch of mathematics, Hilbert's inequality was first demonstrated by David Hilbert
David Hilbert
David Hilbert was a German mathematician. He is recognized as one of the most influential and universal mathematicians of the 19th and early 20th centuries. Hilbert discovered and developed a broad range of fundamental ideas in many areas, including invariant theory and the axiomatization of...

 and later improved by Issai Schur
Issai Schur
Issai Schur was a mathematician who worked in Germany for most of his life. He studied at Berlin...

, who replaced Hilbert's constant with the sharp constant .

Let be complex numbers, Hilbert's inequality is


In 1973, Montgomery & Vaughan reported several generalizations of Hilbert's inequality, considering the bilinear forms


and


where are distinct real numbers modulo 1 (i.e. they belong to distinct classes in the quotient group
Quotient group
In mathematics, specifically group theory, a quotient group is a group obtained by identifying together elements of a larger group using an equivalence relation...

 ) and are distinct real numbers. Montgomery & Vaughan's generalizations of Hilbert's inequality are then given by


and


where and (where is the distance from to the nearest integer and denotes the smallest positive value). Moreover, if and then the following inequalities holds:


and


In their paper they give conditions by which the above sums are allowed to be infinite sum.

See also

  • Hugh Montgomery (mathematician)
  • David Hilbert
    David Hilbert
    David Hilbert was a German mathematician. He is recognized as one of the most influential and universal mathematicians of the 19th and early 20th centuries. Hilbert discovered and developed a broad range of fundamental ideas in many areas, including invariant theory and the axiomatization of...

  • Online book chapter Hilbert’s Inequality and Compensating Difficulties extracted from .
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