In
mathematics, the Shapiro inequality is an
inequality
Inequality may refer to:
Economics
* Attention inequality, unequal distribution of attention across users, groups of people, issues in etc. in attention economy
* Economic inequality, difference in economic well-being between population groups
* ...
proposed by
Harold S. Shapiro
Harold Seymour Shapiro (2 April 1928 – 5 March 2021) was a professor of mathematics at the Royal Institute of Technology in Stockholm, Sweden, best known for inventing the so-called Shapiro polynomials (also known as Golay–Shapiro polyno ...
in 1954.
Statement of the inequality
Suppose
is a
natural number
In mathematics, the natural numbers are those numbers used for counting (as in "there are ''six'' coins on the table") and ordering (as in "this is the ''third'' largest city in the country").
Numbers used for counting are called '' cardinal ...
and
are
positive number
In mathematics, the sign of a real number is its property of being either positive, negative, or zero
0 (zero) is a number representing an empty quantity. In place-value notation such as the Hindu–Arabic numeral system, 0 also se ...
s and:
*
is even and less than or equal to
, or
*
is odd and less than or equal to
.
Then the Shapiro inequality states that
:
where
.
For greater values of
the inequality does not hold and the strict lower bound is
with
.
The initial proofs of the inequality in the pivotal cases
(Godunova and Levin, 1976) and
(Troesch, 1989) rely on numerical computations. In 2002, P.J. Bushell and J.B. McLeod published an analytical proof for
.
The value of
was determined in 1971 by
Vladimir Drinfeld
Vladimir Gershonovich Drinfeld ( uk, Володи́мир Ге́ршонович Дрінфельд; russian: Влади́мир Ге́ршонович Дри́нфельд; born February 14, 1954), surname also romanized as Drinfel'd, is a renowne ...
. Specifically, he proved that the strict lower bound
is given by
, where the function
is the convex hull of
and
. (That is, the region above the graph of
is the
convex hull of the union of the regions above the graphs of '
and
.)
Interior local minima of the left-hand side are always
(Nowosad, 1968).
Counter-examples for higher ''n''
The first counter-example was found by Lighthill in 1956, for
:
:
where
is close to 0.
Then the left-hand side is equal to
, thus lower than 10 when
is small enough.
The following counter-example for
is by Troesch (1985):
:
(Troesch, 1985)
References
*
* {{cite journal , zbl=1018.26010 , last1=Bushell , first1=P.J. , last2=McLeod , first2=J.B. , title=Shapiro's cyclic inequality for even n , journal=J. Inequal. Appl. , volume=7 , number=3 , pages=331–348 , year=2002 , issn=1029-242X , url=ftp://ftp.sam.math.ethz.ch/EMIS/journals/HOA/JIA/40a3.pdf They give an analytic proof of the formula for even
, from which the result for all
follows. They state
as an open problem.
External links
Usenet discussion in 1999(Dave Rusin's notes)
Inequalities