Title
Minimum Number of Monotone Subsequences of Length 4 in Permutations.
Abstract
We show that for every sufficiently large n, the number of monotone subsequences of length four in a permutation on n points is at least [GRAPHICS] . Furthermore, we characterize all permutations on [n] that attain this lower bound. The proof uses the flag algebra framework together with some additional stability arguments. This problem is equivalent to some specific type of edge colourings of complete graphs with two colours, where the number of monochromatic K-4 is minimized. We show that all the extremal colourings must contain monochromatic K-4 only in one of the two colours. This translates back to permutations, where all the monotone subsequences of length four are all either increasing, or decreasing only.
Year
DOI
Venue
2015
10.1017/S0963548314000820
COMBINATORICS PROBABILITY & COMPUTING
Field
DocType
Volume
Discrete mathematics,Graph,Combinatorics,Monochromatic color,Upper and lower bounds,Permutation,Mathematics,Monotone polygon
Journal
24
Issue
ISSN
Citations 
SP4
0963-5483
10
PageRank 
References 
Authors
0.76
22
6
Name
Order
Citations
PageRank
József Balogh186289.91
Ping Hu2324.05
Bernard Lidický318123.68
Oleg Pikhurko431847.03
Balázs Udvari5151.52
Jan Volec6408.27