Mathematics / Math.CO

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Nordhaus-Gaddum for Treewidth

Nordhaus-Gaddum for Treewidth

: ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๋…ธ๋“œ ๊ฐ€๋“œ๋‹ด ์œ ํ˜• ์ •๋ฆฌ๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ํŠธ๋ฆฌ ๋„ˆ๋น„(treewidth)์— ๋Œ€ํ•œ ์ƒˆ๋กœ์šด ๊ด€์ ์„ ์ œ์‹œํ•˜๊ณ  ์žˆ์Šต๋‹ˆ๋‹ค. ์ด๋Š” ํŠนํžˆ ๊ทธ๋ž˜ํ”„ ์ด๋ก ์—์„œ ์ค‘์š”ํ•œ ๋งค๊ฐœ๋ณ€์ˆ˜๋กœ, ๊ทธ๋ž˜ํ”„์˜ ๋ณต์žก์„ฑ์„ ์ธก์ •ํ•˜๋Š” ๋ฐ ํ™œ์šฉ๋ฉ๋‹ˆ๋‹ค. ํŠธ๋ฆฌ ๋„ˆ๋น„์™€ ๊ทธ ์˜๋ฏธ: ํŠธ๋ฆฌ ๋„ˆ๋น„๋Š” ๊ทธ๋ž˜ํ”„ G๋ฅผ ๋ถ€๋ถ„ ๊ทธ๋ž˜ํ”„๋กœ ํฌํ•จํ•  ์ˆ˜ ์žˆ๋Š” k ํŠธ๋ฆฌ(k tree)์˜ ์ตœ์†Œ ์ •์ˆ˜ k๋ฅผ ๋‚˜ํƒ€๋ƒ…๋‹ˆ๋‹ค. ์ด๋Š” ํŠธ๋ฆฌ ๋ถ„ํ•ด(tree decomposition)๋ฅผ ํ†ตํ•ด ์ •์˜๋˜๋ฉฐ, ๊ทธ๋ž˜ํ”„์˜ ๋ณต์žก์„ฑ์„ ์ธก์ •ํ•˜๋Š” ๋ฐ ์ค‘์š”ํ•œ ์—ญํ• ์„ ํ•ฉ๋‹ˆ๋‹ค. ๋…ธ๋“œ ๊ฐ€๋“œ๋‹ด ์œ ํ˜• ์ •๋ฆฌ์™€ ํŠธ๋ฆฌ ๋„ˆ๋น„: ๋ณธ ๋…ผ๋ฌธ์—์„œ ์ œ์‹œ๋œ ๋…ธ๋“œ ๊ฐ€๋“œ๋‹ด

Mathematics Computer Science Discrete Mathematics
VC dimension of ellipsoids

VC dimension of ellipsoids

: ๋ณธ ๋…ผ๋ฌธ์€ ์—˜๋ฆฝ์†Œ์ด๋“œ์˜ ๋ณต์žก์„ฑ์„ ์ธก์ •ํ•˜๋Š” VC ์ฐจ์›์— ๋Œ€ํ•œ ์‹ฌ์ธต์ ์ธ ์—ฐ๊ตฌ๋ฅผ ์ˆ˜ํ–‰ํ•œ๋‹ค. ์ด๋Š” ํ•™์Šต ์ด๋ก ์—์„œ ์ค‘์š”ํ•œ ๊ฐœ๋…์œผ๋กœ, ๋ฐ์ดํ„ฐ ๋ถ„์„ ๋ฐ ๋ชจ๋ธ ์„ ํƒ์— ํ™œ์šฉ๋œ๋‹ค. 1. VC ์ฐจ์›์˜ ์ •์˜์™€ ์ค‘์š”์„ฑ VC ์ฐจ์›์€ ์ง‘ํ•ฉ์ด ์–ผ๋งˆ๋‚˜ ๋ณต์žกํ•œ ํ˜•ํƒœ๋ฅผ ๊ฐ€์งˆ ์ˆ˜ ์žˆ๋Š”์ง€๋ฅผ ์ธก์ •ํ•˜๋Š” ์ง€ํ‘œ๋กœ, ๊ฒฝํ—˜์  ๊ณผ์ • ์ด๋ก , ํ†ต๊ณ„ ๋ฐ ๊ณ„์‚ฐ ํ•™์Šต ์ด๋ก , ๊ทธ๋ฆฌ๊ณ  ์ด์‚ฐ ๊ธฐํ•˜ํ•™ ๋“ฑ ๋‹ค์–‘ํ•œ ๋ถ„์•ผ์—์„œ ํ™œ์šฉ๋œ๋‹ค. ํŠนํžˆ, VC ์ฐจ์›์€ ๋ฐ์ดํ„ฐ์˜ ๋ณต์žก์„ฑ์„ ์ธก์ •ํ•˜๊ณ  ๋ชจ๋ธ ์„ ํƒ์— ์ค‘์š”ํ•œ ์—ญํ• ์„ ํ•œ๋‹ค. 2. ์—˜๋ฆฝ์†Œ์ด๋“œ์™€ ๊ฐ€์šฐ์‹œ์•ˆ ํ˜ผํ•ฉ ๋ชจ๋ธ ์—˜๋ฆฝ์†Œ์ด๋“œ๋Š” d์ฐจ์› ๊ณต๊ฐ„์—์„œ ์ •์˜๋˜๋Š” ์ง‘ํ•ฉ์œผ๋กœ,

Mathematics Statistics Computer Science Machine Learning
Complexity of Bondage and Reinforcement

Complexity of Bondage and Reinforcement

๋ณธ ๋…ผ๋ฌธ์€ ์ง€๋ฐฐ ์ง‘ํ•ฉ๊ณผ ๊ด€๋ จ๋œ ์—ฌ๋Ÿฌ ๋งค๊ฐœ๋ณ€์ˆ˜, ํŠนํžˆ ๊ฒฐํ•ฉ ์ˆซ์ž์™€ ๊ฐ•ํ™” ์ˆซ์ž์˜ ๋ณต์žก์„ฑ์„ ๋ถ„์„ํ•˜๊ณ  ์žˆ๋‹ค. ์ด๋Ÿฌํ•œ ๊ฐœ๋…๋“ค์€ ๊ทธ๋ž˜ํ”„ ์ด๋ก ์—์„œ ์ค‘์š”ํ•œ ์—ญํ• ์„ ํ•˜๋ฉฐ, ํŠนํžˆ NP ์™„์ „์„ฑ ๋ฌธ์ œ์— ๋Œ€ํ•œ ์ดํ•ด๋ฅผ ๊นŠ๊ฒŒ ํ•œ๋‹ค. 1. ์ง€๋ฐฐ ์ง‘ํ•ฉ๊ณผ ๊ด€๋ จ ๋งค๊ฐœ๋ณ€์ˆ˜ ์ง€๋ฐฐ ์ง‘ํ•ฉ์€ ๊ทธ๋ž˜ํ”„ G (V, E)์˜ ๋ชจ๋“  ๊ผญ์ง“์ ์ด ํ•ด๋‹น ์ง‘ํ•ฉ ๋‚ด์˜ ์ธ์ ‘ํ•œ ๊ผญ์ง“์ ์— ํฌํ•จ๋˜๋Š” ์ตœ์†Œ ์ง‘ํ•ฉ์ด๋‹ค. ์ด๋Š” ๊ทธ๋ž˜ํ”„์—์„œ ์ค‘์š”ํ•œ ์ •๋ณด๋ฅผ ํšจ์œจ์ ์œผ๋กœ ์ „๋‹ฌํ•˜๊ฑฐ๋‚˜ ์ปค๋ฒ„ํ•˜๋Š” ๋ฐ ์‚ฌ์šฉ๋œ๋‹ค. ์ง€๋ฐฐ ์ˆซ์ž ฮณ(G)๋Š” ์ด๋Ÿฌํ•œ ์ตœ์†Œ ์ง‘ํ•ฉ์˜ ํฌ๊ธฐ๋ฅผ ๋‚˜ํƒ€๋‚ด๋ฉฐ, ์ด๋ฅผ ๊ณ„์‚ฐํ•˜๋Š” ๋ฌธ์ œ๋Š” NP ์™„์ „์ž„์ด ์•Œ๋ ค์ ธ ์žˆ๋‹ค. ๊ฒฐํ•ฉ

Mathematics Computational Complexity Computer Science
On the Intersection of All Critical Sets of a Unicyclic Graph

On the Intersection of All Critical Sets of a Unicyclic Graph

: ๋ณธ ๋…ผ๋ฌธ์€ ์œ ์‚ฌ์ดํด์  ๊ทธ๋ž˜ํ”„, ์ฆ‰ ๋‹จ์ผ ์‚ฌ์ดํด์„ ๊ฐ–๋Š” ์—ฐ๊ฒฐ ๊ทธ๋ž˜ํ”„์—์„œ ํ•ต์‹ฌ(core), ์ฝ”๋กœ๋‚˜(corona), ๊ทธ๋ฆฌ๊ณ  ker(G) ์ง‘ํ•ฉ๋“ค ๊ฐ„์˜ ๊ด€๊ณ„์— ๋Œ€ํ•ด ๊นŠ์ด ์žˆ๋Š” ๋ถ„์„์„ ์ œ๊ณตํ•œ๋‹ค. ์ด๋Ÿฌํ•œ ๊ทธ๋ž˜ํ”„๋“ค์€ ์ด๋ก ์ ์œผ๋กœ ์ค‘์š”ํ•œ ์œ„์น˜๋ฅผ ์ฐจ์ง€ํ•˜๋ฉฐ, ํŠนํžˆ ๊ทธ๋“ค์˜ ๋…๋ฆฝ ์ง‘ํ•ฉ๊ณผ ๋งค์นญ์— ๋Œ€ํ•œ ์„ฑ์งˆ์€ ๊ทธ๋ž˜ํ”„ ์ด๋ก ์—์„œ ํ•ต์‹ฌ์ ์ธ ์—ญํ• ์„ ํ•œ๋‹ค. ๋…ผ๋ฌธ์—์„œ๋Š” ๋จผ์ € ํ•ต์‹ฌ(core)๊ณผ ์ฝ”๋กœ๋‚˜(corona)์˜ ์ •์˜๋ฅผ ์ œ์‹œํ•œ๋‹ค. ํ•ต์‹ฌ์€ ๋ชจ๋“  ์ตœ๋Œ€ ๋…๋ฆฝ ์ง‘ํ•ฉ๋“ค์˜ ๊ต์ง‘ํ•ฉ์ด๊ณ , ์ฝ”๋กœ๋‚˜๋Š” ์ด๋Ÿฌํ•œ ์ง‘ํ•ฉ๋“ค์˜ ํ•ฉ์ง‘ํ•ฉ์ด๋‹ค. ker(G)๋Š” G์˜ ์ค‘์š”ํ•œ ๋…๋ฆฝ ์ง‘ํ•ฉ๋“ค์˜ ๊ต์ง‘ํ•ฉ์œผ๋กœ ์ •

Mathematics Computer Science Discrete Mathematics
No Image

Monochromatic Progressions in Random Colorings

: 1. ๋ฐ˜๋”์™€๋ฅด๋ด ์ •๋ฆฌ์™€ W(k) ๋ฐ˜๋”์™€๋ฅด๋ด ์ •๋ฆฌ๋Š” ๋žจ์ง€ ์ด๋ก ์—์„œ ์ค‘์š”ํ•œ ์œ„์น˜๋ฅผ ์ฐจ์ง€ํ•˜๋ฉฐ, ๋ชจ๋“  ์–‘์˜ ์ •์ˆ˜ k์— ๋Œ€ํ•ด W(k)๋ผ๋Š” ์ƒํ•œ์„ ์„ ์ œ์‹œํ•ฉ๋‹ˆ๋‹ค. ์ด๋Š” {1, 2, ..., W(k)}์˜ 2์ƒ‰ ๋ถ„๋ฅ˜์—์„œ kํ•ญ ์•„๋ ˆํŠธ๋ฆญ ์ง„ํ–‰์ด ๋ฐ˜๋“œ์‹œ ๋ชจ๋…ธํฌ๋กฌ์œผ๋กœ ๋‚˜ํƒ€๋‚œ๋‹ค๋Š” ๊ฒƒ์„ ์˜๋ฏธํ•ฉ๋‹ˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ W(k)์˜ ์ •ํ™•ํ•œ ๊ฐ’์€ k๊ฐ€ ์ž‘์„ ๋•Œ๋งŒ ์•Œ๋ ค์ ธ ์žˆ์œผ๋ฉฐ, k๊ฐ€ ์ปค์งˆ์ˆ˜๋ก ์ด ๊ฐ’์„ ๊ตฌํ•˜๋Š” ๊ฒƒ์ด ๋งค์šฐ ์–ด๋ ค์›Œ์ง‘๋‹ˆ๋‹ค. 2. ํ™•๋ฅ ์  ์ ‘๊ทผ: N+(k)์™€ N (k) N+(k)๋Š” {1, 2, ..., N+(k)}์˜ 2์ƒ‰ ๋ถ„๋ฅ˜์—์„œ kํ•ญ ์•„๋ ˆํŠธ๋ฆญ ์ง„ํ–‰์ด ํฌํ•จ๋  ํ™•๋ฅ ์ด

Computer Science Mathematics Discrete Mathematics
On a property of the $n$-dimensional cube

On a property of the $n$-dimensional cube

๋ณธ ๋…ผ๋ฌธ์€ ๊ณ ์ฐจ์› ๊ทธ๋ž˜ํ”„ ์ด๋ก ์—์„œ ์ค‘์š”ํ•œ ๋ฌธ์ œ ์ค‘ ํ•˜๋‚˜์ธ n์ฐจ์› ํ๋ธŒ์˜ ๋ถ€๋ถ„ ์ง‘ํ•ฉ์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋ฅผ ์ˆ˜ํ–‰ํ•˜๊ณ  ์žˆ๋‹ค. ํŠนํžˆ, n โ‰ฅ 4์ผ ๋•Œ, |V'| โ‰ฅ 2^(n 1) + 1์ธ ๋ชจ๋“  ๋ถ€๋ถ„ ์ง‘ํ•ฉ V'์— ๋Œ€ํ•ด ํด๋ผ์šฐ ๋˜๋Š” ๋‹จ์ˆœ ์ˆœํ™˜์„ ์œ ๋„ํ•˜๋Š” ์ •์ ๋“ค์˜ ์กด์žฌ๋ฅผ ์ฆ๋ช…ํ•œ๋‹ค. ์„œ๋ก  ๋ฐ ์ •์˜ ๋…ผ๋ฌธ์€ ๊ทธ๋ž˜ํ”„ ์ด๋ก ์—์„œ ์ค‘์š”ํ•œ ๊ฐœ๋…๋“ค์„ ์†Œ๊ฐœํ•˜๊ณ , n์ฐจ์› ํ๋ธŒ Qn๊ณผ ํด๋ผ์šฐ(K1,3)์˜ ์ •์˜๋ฅผ ์ œ๊ณตํ•œ๋‹ค. ํŠนํžˆ, n์ฐจ์› ํ๋ธŒ๋Š” ๊ฐ ์ฐจ์›๋งˆ๋‹ค ๋‘ ๊ฐœ์˜ ๊ฐ’์„ ๊ฐ€์งˆ ์ˆ˜ ์žˆ๋Š” ์ •์  ์ง‘ํ•ฉ์œผ๋กœ ๊ตฌ์„ฑ๋˜๋ฉฐ, ํด๋ผ์šฐ๋Š” ์ค‘์‹ฌ ์ •์ ์„ ํฌํ•จํ•˜๋Š” ์™„์ „ ์ด๋ถ„ ๊ทธ๋ž˜ํ”„ K1,3์„ ์˜๋ฏธํ•œ

Mathematics Computer Science Discrete Mathematics
A conjecture on independent sets and graph covers

A conjecture on independent sets and graph covers

๋ณธ ๋…ผ๋ฌธ์€ ๊ทธ๋ž˜ํ”„ ์ด๋ก ์˜ ํ•ต์‹ฌ ๊ฐœ๋…์ธ ๋…๋ฆฝ ์ง‘ํ•ฉ๊ณผ ์ปค๋ฒ„๋ฅผ ๋‹ค๋ฃจ๋ฉฐ, ํŠนํžˆ M ์ปค๋ฒ„์™€ ๋ฒ ํ…Œ ๊ทผ์‚ฌ(Bethe approximation) ์‚ฌ์ด์˜ ๊ด€๊ณ„๋ฅผ ํƒ๊ตฌํ•œ๋‹ค. ์ด๋Ÿฌํ•œ ์—ฐ๊ตฌ๋Š” ํ†ต๊ณ„ ๋ฌผ๋ฆฌํ•™์—์„œ ์ค‘์š”ํ•œ ์—ญํ• ์„ ํ•˜๋Š” ๋ถ„ํ•  ํ•จ์ˆ˜(partition function)์™€ ์ž์œ  ์—๋„ˆ์ง€(free energy)์— ๋Œ€ํ•œ ์ดํ•ด๋ฅผ ํ™•์žฅํ•˜๋Š” ๋ฐ ๊ธฐ์—ฌํ•œ๋‹ค. 1. ๋‹ค๋ณ€์ˆ˜ ๋…๋ฆฝ ์ง‘ํ•ฉ ๋‹คํ•ญ์‹๊ณผ M ์ปค๋ฒ„ ๋…ผ๋ฌธ์€ ๊ทธ๋ž˜ํ”„ G์˜ ๋‹ค๋ณ€์ˆ˜ ๋…๋ฆฝ ์ง‘ํ•ฉ ๋‹คํ•ญ์‹์„ ์ •์˜ํ•˜๊ณ , ์ด๋ฅผ ํ†ตํ•ด ๋…๋ฆฝ ์ง‘ํ•ฉ์˜ ํฌ๊ธฐ์— ๋”ฐ๋ฅธ ๊ฐ€์ค‘์น˜๋ฅผ ํ‘œํ˜„ํ•œ๋‹ค. ์ด ๋‹คํ•ญ์‹์€ G์˜ ๋ชจ๋“  ๋…๋ฆฝ ์ง‘ํ•ฉ I์— ๋Œ€ํ•ด x^{|I|

Mathematics Computer Science Discrete Mathematics
No Image

Guaranteed successful strategies for a square achievement game on an n by n grid

์ด ๋…ผ๋ฌธ์€ ์ •์‚ฌ๊ฐํ˜• ๋‹ฌ์„ฑ ๊ฒŒ์ž„์—์„œ ์ตœ์ ์˜ ํ”Œ๋ ˆ์ด ์ „๋žต์— ๋Œ€ํ•œ ์‹ฌ๋„ ์žˆ๋Š” ๋ถ„์„์„ ์ œ๊ณตํ•œ๋‹ค. ์ด ๊ฒŒ์ž„์€ n x n ๊ทธ๋ฆฌ๋“œ ์œ„์—์„œ ๋‘ ํ”Œ๋ ˆ์ด์–ด๊ฐ€ 'O'์™€ 'X'๋ฅผ ๋ฒˆ๊ฐˆ์•„ ๋ฐฐ์น˜ํ•˜๋ฉฐ, ์ฒซ ๋ฒˆ์งธ ํ”Œ๋ ˆ์ด์–ด๋Š” ์ˆ˜ํ‰ ๋ฐ ์ˆ˜์ง ๋ณ€์˜ ๋ชจ์„œ๋ฆฌ์— 4๊ฐœ์˜ ์…€์„ ์ ์œ ํ•˜์—ฌ ์Šน๋ฆฌ๋ฅผ ๋‹ฌ์„ฑํ•ด์•ผ ํ•œ๋‹ค. ๋…ผ๋ฌธ์€ SQRGAME2๋ผ๋Š” ์ปดํ“จํ„ฐ ํ”„๋กœ๊ทธ๋žจ์„ ์‚ฌ์šฉํ•ด n์ด 3, 4, 5์ผ ๋•Œ ๊ฐ ํ”Œ๋ ˆ์ด์–ด๊ฐ€ ์ตœ์ ์˜ ์ „๋žต์œผ๋กœ ๊ฒŒ์ž„์—์„œ ์–ด๋–ป๊ฒŒ ์ด๊ธธ ์ˆ˜ ์žˆ๋Š”์ง€ ๋ถ„์„ํ•œ๋‹ค. ๊ฒŒ์ž„์˜ ๊ทœ์น™๊ณผ ์ง„ํ–‰ ๋ฐฉ์‹์— ๋Œ€ํ•œ ์ž์„ธํ•œ ์„ค๋ช…์€ ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค. G๋Š” 0๋ถ€ํ„ฐ (์ ์–ด๋„) n 1๊นŒ์ง€์˜ ์ •์ˆ˜ ์ธ๋ฑ์Šค ๋ฒ”์œ„๋ฅผ ๊ฐ€

Mathematics Computer Science Discrete Mathematics
Total coloring of pseudo-outerplanar graphs

Total coloring of pseudo-outerplanar graphs

: 1. ์ด ์ƒ‰์น  ๋ฌธ์ œ์™€ ๊ทธ ์ค‘์š”์„ฑ ์ด ์ƒ‰์น  ๋ฌธ์ œ๋Š” ๊ทธ๋ž˜ํ”„ ์ด๋ก ์—์„œ ์ค‘์š”ํ•œ ์œ„์น˜๋ฅผ ์ฐจ์ง€ํ•˜๋ฉฐ, ๊ฐ ์ •์ ๊ณผ ๊ฐ„์„ ์— ๊ณ ์œ ํ•œ ์ƒ‰์ƒ์„ ํ• ๋‹นํ•˜๋Š” ๋ฐฉ์‹์œผ๋กœ ๊ทธ๋ž˜ํ”„์˜ ๊ตฌ์กฐ์  ํŠน์„ฑ์„ ์ดํ•ดํ•˜๊ณ  ๋ถ„์„ํ•ฉ๋‹ˆ๋‹ค. ํŠนํžˆ, ์ด ์ƒ‰์น  ์ถ”์ธก์€ ๊ทธ๋ž˜ํ”„์˜ ์ตœ๋Œ€ ์ฐจ์ˆ˜ ฮ”(G)์™€ ๊ด€๋ จ๋œ ์ค‘์š”ํ•œ ๋ฌธ์ œ๋กœ, ์ด ์ถ”์ธก์ด ์ฆ๋ช…๋˜๋ฉด ๋งŽ์€ ๊ทธ๋ž˜ํ”„ ํด๋ž˜์Šค์— ๋Œ€ํ•œ ์ด ์ƒ‰์ƒ ์ˆ˜๋ฅผ ๊ฒฐ์ •ํ•˜๋Š” ๋ฐ ๋„์›€์ด ๋ฉ๋‹ˆ๋‹ค. 2. ์œ„์ƒ์  ์™ธํŒ ๊ทธ๋ž˜ํ”„์˜ ์ •์˜ ๋ฐ ํŠน์„ฑ ์œ„์ƒ์  ์™ธํŒ ๊ทธ๋ž˜ํ”„๋Š” ๊ฐ ๋ธ”๋ก์ด ๊ณ ์ •๋œ ์› ์œ„์—์„œ ์ •์ ๋“ค์„ ๋ฐฐ์น˜ํ•˜๊ณ , ๊ฐ„์„ ๋“ค์ด ์›์˜ ๋””์Šคํฌ ๋‚ด๋ถ€์—์„œ ์„œ๋กœ ๊ต์ฐจํ•˜์ง€ ์•Š๋„๋ก ๋ฐฐ์น˜๋  ์ˆ˜ ์žˆ๋Š” ๊ทธ๋ž˜

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