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License: MIT License
Some Computer Science notes I thought I would share with others
License: MIT License
r(k,l) = binom (k+l-2) choose (k-1)
viz http://mj.ucw.cz/papers/ramsey.pdf
-- Dukaz T(n) = \lfloor n^2 / 4 \rfloor
-- Dukaz T(n) = \lfloor n^2 / 4 \rfloor
ještě nám ukazoval, že graf s maximálním počtem hran bez trojúhelníku je právě K_n/2,n/2 - důkaz = zamyslet se nad důkazem té rovnosti
poznamka k predchozi - T(n) oznacoval jako max pocet hran v grafu s n vrcholy bez K3
-- a tedy Důkaz $|E(G)| \leq \frac{1}{2} \left( n^\frac{3}{2} + n \right)
vezměme si množinu
Nahlédneme, že pro libovolnou dvojici
Dále nahlédneme, že pro
Pokud budou tedy
$$ \sum_{i=1}^n (d_i - 1) \leq \sqrt{\sum_{i=1}^n (d_i - 1)^2} \sqrt{\sum_{i=1}^n} \leq \sqrt{n^2} \sqrt{n} \leq n^{\frac{3}{2}}$$
-- tenhle důkaz je ošklivý, tak si ho radši ještě projdi, Medvěd nám ho dával takhle. Ten už se mi narozdíl od předchozího nelíbí.
Ekvivalence:
PoVyKoSy - speciální orientované stromy, tak že ex u: deg_out(u) = 0 a pro vsechna v z V{u} je deg_out(v) = 1. V dukazu MJ ukazal vztah mezi poctem stromu na n vrcholech a poctem techto stromu a pak tyhle stromy spocital
Ramsey - ukazoval dolni odhad Ramseyova cisla, t.z. R(k,k) >= 2^(k/2) --- pravdepodobnosti metoda, vezmes graf s nahodnym obarvenim, P[je k-klika] = 2^-(k/2), to samy s druhou klikou, pak pouzijes P(A u B) <= P(A) + P(B) -> P[ex. co chceme] = (n choose k) * 2 * 2^-(k/2) a chces ukazat, kdy je to mensi nez jedna, vyjde prave n < 2^(k/2)
V důkazu jsou použity opačné odhady, je třeba ho opravit.
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