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1 vote

### Good examples of "two is easy, three is hard" in computational sciences

MaxEnt distribution subject to equality constraints on cumulants is easy to compute for constraints on first 2 cumulants (closed form solution), hard for constraints on first 3 cumulants. In the ...
• 1,159
1 vote

### Good examples of "two is easy, three is hard" in computational sciences

The non-negative rank of an entrywise non-negative matrix $A\in\mathbb{R}^{m\times n}_{\geq 0}$, i.e., the minimum $r$ for which a factorization $A = BC$ exists with \$B\in\mathbb{R}^{m\times r}_{\geq ...
• 8,785