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Beck-Fiala Conjecture


The Beck-Fiala conjecture asserts that there is an absolute constant C>0 such that every finite family F of subsets of a finite set X, with each element in at most t members, satisfies

 disc(F)<=Csqrt(t)

for every positive integer t. Here disc(F) is the set system discrepancy. The parameter t bounds the number of sets containing an element, rather than the size of each set (Beck and Fiala 1981).

The Beck-Fiala theorem gives the classical bound disc(F)<=2t-1 for t>=1 (Beck and Fiala 1981). Guo et al. (2026) report a bound with square-root dependence

 disc(F)<3sqrt(2pit).

It follows from their Komlós conjecture result by dividing each column of the incidence matrix, with rows indexed by sets and columns by elements, by sqrt(t). Every resulting column has Euclidean norm at most 1. The constant is not asserted to be optimal, and the argument does not establish an algorithm running in polynomial time. When t=0, every member of F is empty and the discrepancy is zero.


See also

Komlós Conjecture, Set System Discrepancy, Vector Balancing

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References

Beck, J. and Fiala, T. " 'Integer-Making' Theorems." Disc. Appl. Math. 3, 1-8, 1981. https://doi.org/10.1016/0166-218X(81)90022-6.Guo, S.; Fang, E. X.; and Lu, J. "Vector Balancing via Directional Total Variation." 10 Sep 2026. https://arxiv.org/abs/2609.11189.

Cite this as:

Weisstein, Eric W. "Beck-Fiala Conjecture." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Beck-FialaConjecture.html

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