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Around 1932 mathematician [[Paul_Erdős]] conjectured that for any infinite ±1-sequence <math> |
Around 1932 mathematician [[Paul_Erdős]] conjectured that for any infinite ±1-sequence <math>\textstyle\langle x_1, x_2, ..\rangle </math> and any integer ''C'' there exist integers ''k'' and ''d'' such that: |
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: <math> \left| \sum_{i=1}^k x_{id} \right| > C </math> |
: <math> \left| \sum_{i=1}^k x_{id} \right| > C </math> |
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The Erdős Discrepancy Problem asks for a proof or disproof of this conjecture. |
The Erdős Discrepancy Problem asks for a proof or disproof of this conjecture. |
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A |
A SAT-solver-based proof <ref>[http://arxiv.org/pdf/1402.2184v2.pdf], featured in [http://www.newscientist.com/article/dn25068-wikipediasize-maths-proof-too-big-for-humans-to-check.html]</ref> has shown that every sequence ''S'' of 1161 or more elements satisfies the conjecture in the special case ''C''=2: this constitutes a proof of the conjecture for ''C''≤2. {{Asof|2014|February}}, this is the best such bound available. |
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{{Asof|2010|October}}, this problem is currently being studied by the [[Polymath Project]] [http://michaelnielsen.org/polymath1/index.php?title=The_Erd%C5%91s_discrepancy_problem]. |
{{Asof|2010|October}}, this problem is currently being studied by the [[Polymath Project]] [http://michaelnielsen.org/polymath1/index.php?title=The_Erd%C5%91s_discrepancy_problem]. |
Revision as of 07:15, 18 February 2014
In mathematics, a ±1–sequence is a sequence of numbers, each of which is either 1 or −1. One example is the sequence (x1, x2, x3, ...), where xi = (−1)i+1.
Such sequences are commonly studied in discrepancy theory.
Erdős discrepancy problem
Around 1932 mathematician Paul_Erdős conjectured that for any infinite ±1-sequence and any integer C there exist integers k and d such that:
The Erdős Discrepancy Problem asks for a proof or disproof of this conjecture.
A SAT-solver-based proof [1] has shown that every sequence S of 1161 or more elements satisfies the conjecture in the special case C=2: this constitutes a proof of the conjecture for C≤2. As of February 2014[update], this is the best such bound available.
As of October 2010[update], this problem is currently being studied by the Polymath Project [3].
Barker codes
A Barker code is a sequence of N values of +1 and −1,
- for j = 1, 2, …, N
such that
for all .[2]
Barker codes of length 11 and 13 are used in direct-sequence spread spectrum and pulse compression radar systems because of their low autocorrelation properties.
See also
Notes
References
- Chazelle, Bernard. The Discrepancy Method: Randomness and Complexity. Cambridge University Press. ISBN 0-521-77093-9.
External links
- The Erdős discrepancy problem – Polymath Project