Boolean Pythagorean triples problem: Difference between revisions

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{{short description|Can one split the integers into two sets such that every Pythagorean triple spans both?}}

The '''Boolean Pythagorean triples problem''' is a problem from [[Ramsey theory]] about whether the [[Pythagoreannatural triplenumber|positive integers]]s, whichcan asksbe ifcolored itred isand possibleblue toso colorthat eachno of[[Pythagorean thetriple]]s positiveconsist integersof eitherall red or all blue, somembers. thatThe noBoolean Pythagorean tripletriples ofproblem integerswas ''a'',solved ''b'',by ''c''[[Marijn Heule]], satisfyingOliver <math>a^2+b^2=c^2</math>Kullmann areand all[[Victor theW. sameMarek]] color.in ForMay example2016 through a [[computer-assisted proof]], inwhich theshowed Pythagoreanthat triplesuch 3,a 4coloring andis 5only (<math>3^2+4^2=5^2</math>),possible ifup 3to andthe 4number are7824.<ref coloredname="nature">{{Cite red,journal|last=Lamb|first=Evelyn|date=26 thenMay 52016|title=Two-hundred-terabyte mustmaths beproof coloredis bluelargest ever|journal=Nature|doi=10.1038/nature.2016.19990|volume=534|issue=7605 |pages=17–18|pmid=27251254|bibcode=2016Natur.534...17L|doi-access=free}}</ref>

==Statement==

The problem was solved by Marijn Heule, Oliver Kullmann and [[Victor W. Marek]] in May 2016 through a [[computer-assisted proof]].<ref name="nature">{{Cite journal|last=Lamb|first=Evelyn|date=26 May 2016|title=Two-hundred-terabyte maths proof is largest ever|url=http://www.nature.com/news/two-hundred-terabyte-maths-proof-is-largest-ever-1.19990|journal=Nature|doi=10.1038/nature.2016.19990|volume=534|pages=17–18|pmid=27251254|bibcode=2016Natur.534...17L|doi-access=free}}</ref> They showed that such a coloring is only possible up to the number 7824. The actual statement of the theorem proved is

The problem asks if it is possible to color each of the positive integers either red or blue, so that no Pythagorean triple of integers ''a'', ''b'', ''c'', satisfying <math>a^2+b^2=c^2</math> are all the same color.

{{math theorem| The set {1, . . . , 7824} can be partitioned into two parts, such that no part contains a Pythagorean triple, while this is impossible for {1, . . . , 7825}.<ref name="arXiv"/>}}

For example, in the Pythagorean triple 3, 4, and 5 (<math>3^2+4^2=5^2</math>), if 3 and 4 are colored red, then 5 must be colored blue.

There are {{nowrap|2⁷⁸²⁵ ≈ 3.63×10²³⁵⁵}} possible coloring combinations for the numbers up to [[7825 (number)|7825]]. These possible colorings were logically and algorithmically narrowed down to around a trillion (still highly complex) cases, and those were examined using a [[Boolean satisfiability]] solver. Creating the proof took about 4 CPU-years of computation over a period of two days on the Stampede supercomputer at the [[Texas Advanced Computing Center]] and generated a 200 terabyte propositional proof, which was compressed to 68 gigabytes.

==Solution==

The paper describing the proof was published in the SAT 2016 conference,<ref name="arXiv">{{Cite conference|last=Heule|first=Marijn J. H.|last2=Kullmann|first2=Oliver|last3=Marek|first3=Victor W.|author3-link=Victor W. Marek|year=2016|contribution=Solving and Verifying the Boolean Pythagorean Triples problem via Cube-and-Conquer |arxiv=1605.00723|doi=10.1007/978-3-319-40970-2_15|series=Lecture Notes in Computer Science|volume=9710|pages=228–245|title=Theory and Applications of Satisfiability Testing – SAT 2016: 19th International Conference, Bordeaux, France, July 5-8, 2016, Proceedings|editor1-first=Nadia|editor1-last=Creignou|editor2-first=Daniel|editor2-last=Le Berre}}</ref> where it won the best paper award.<ref>[http://sat2016.labri.fr/ SAT 2016]</ref>

[[Marijn Heule]], Oliver Kullmann and Victor W. Marek showed that such a coloring is only possible up to the number 7824. The actual statement of the theorem proved is

{{math theorem| The set {1, . . . , 7824} can be partitioned into two parts, such that no part contains a Pythagorean triple, while this is impossible for {1, . . . , 7825}.<ref name="arXiv"/>}}

}}

There are {{nowrap|2⁷⁸²⁵ ≈ 3.63×10²³⁵⁵}} possible coloring combinations for the numbers up to [[7825 (number)|7825]]. These possible colorings were logically and algorithmically narrowed down to around a trillion (still highly complex) cases, and those, expressed as [[Boolean satisfiability]] problems, were examined using a [[BooleanSAT satisfiabilitysolver]] solver. Creating the proof took about 4 CPU-years of computation over a period of two days on the Stampede supercomputer at the [[Texas Advanced Computing Center]] and generated a 200 terabyte propositional proof, which was compressed to 68 gigabytes.

In the 1980s [[Ronald Graham]] offered a $100 prize for the solution of the problem, which has now been awarded to Marijn Heule.<ref name="nature"/>

The paper describing the proof was published in the SAT 2016 conference,<ref name="arXiv">{{Cite conference|lastlast1=Heule|firstfirst1=Marijn J. H.|last2=Kullmann|first2=Oliver|last3=Marek|first3=Victor W.|author3-link=Victor W. Marek|year=2016|contribution=Solving and Verifying the Boolean Pythagorean Triples problem via Cube-and-Conquer |arxiv=1605.00723|doi=10.1007/978-3-319-40970-2_15|series=Lecture Notes in Computer Science|volume=9710|pages=228–245|title=Theory and Applications of Satisfiability Testing – SAT 2016: 19th International Conference, Bordeaux, France, July 5-8, 2016, Proceedings|editor1-first=Nadia|editor1-last=Creignou|editor2-first=Daniel|editor2-last=Le Berre}}</ref> where it won the best paper award.<ref>[http://sat2016.labri.fr/ SAT 2016]</ref> The figure below shows a possible family of colorings for the set {1,...,7824} with no monochromatic Pythagorean triple, and the white squares can be colored either red or blue while still satisfying this condition.

[[File:Ptn-7824-zoom-2.png|alt=|center|400x400px]]

==Prize==

In the 1980s [[Ronald Graham]] offered a $100 prize for the solution of the problem, which has now been awarded to [[Marijn Heule]].<ref name="nature"/>

== Generalizations ==

As of 2018, the problem is still open for more than 2 colors, that is, if there exists a ''k''-coloring (''k'' ≥ 3) of the positive integers such that no Pythagorean triples are the same color.<ref>{{Cite journal|last1=Eliahou|first1=Shalom|last2=Fromentin|first2=Jean|last3=Marion-Poty|first3=Virginie|last4=Robilliard|first4=Denis|date=2018-10-02|title=Are Monochromatic Pythagorean Triples Unavoidable under Morphic Colorings?|url=https://www.tandfonline.com/doi/full/10.1080/10586458.2017.1306465|journal=Experimental Mathematics|language=en|volume=27|issue=4|pages=419–425|doi=10.1080/10586458.2017.1306465|issn=1058-6458|arxiv=1605.00859|s2cid=19035265 }}</ref>

== See also ==