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This is a branch that includes: computational complexity theory; complexity classes, NP-completeness and other completeness concepts; oracle analogues of complexity classes; complexity-theoretic computational models; regular languages; context-free languages; Komolgorov Complexity and so on.

7 votes
Accepted

NP Hardness proof for permanent of 0-1 matrix

Les Valiant's original paper is beautifully written. EDIT A simpler proof, with a nice explanation (see Section 3) is given by Ben-Dor and Halevy
Igor Rivin's user avatar
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1 vote

Complexity of Max Bisection on cubic planar graphs?

I am pretty sure that the result in http://rutcor.rutgers.edu/pub/rrr/reports2006/23_2006.pdf tells us that Max-Bisection is NP-hard on bounded degree planar graphs (however, I think the bound is big …
Igor Rivin's user avatar
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1 vote

Pseudorandom Functions / Pseudorandom Permutations

To expand very slightly upon @Steve's words of wisdom, see http://en.wikipedia.org/wiki/Feistel_cipher
Igor Rivin's user avatar
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2 votes
Accepted

testing singularity of integer matrices

This is addressed in Storjohann's paper on computing Smith Normal Form.
Igor Rivin's user avatar
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2 votes

Quick tests for Self complementary vertex transitive graphs

A fairly comprehensive survey as of 13 years ago is given in Alastair Farrugia's Master's thesis (see chapter 3, in particular).
Igor Rivin's user avatar
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5 votes

Computational complexity of Knot polynomials

Complexity: Knots, Colourings and Counting By D. J. A. Welsh Has pretty extensive information.
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15 votes

Computational complexity of computing homotopy groups of spheres

It is shown by D. J. Anick in The computation of rational homotopy groups is #℘-hard. Computers in geometry and topology, Proc. Conf., Chicago/Ill. 1986, Lect. Notes Pure Appl. Math. 114, 1–56, 1989. …
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2 votes

How long does it take to compute a class number?

J. Buchmann and M. Pohst in a 1989 paper show that the class group can be computed in time of order $D^{1+\epsilon},$ where $D$ is the discriminant.
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6 votes

Are there any efficient (polynomial time) algorithms for finding if a multivariate quadratic...

I might be misunderstanding the question, but if the equation is homogeneous, then zero is a solution, if the homogeneous (degree 2) part is an indefinite quadratic form, then the equation has a solut …
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4 votes

Examples of ubiquitous objects that are hard to find?

A random pair of elements of $\mathop{SL}(n, \mathbb{Z})$ (where random is defined by taking a generating set, and picking two random long words) almost certainly (meaning, with probability approachin …
2 votes

Is unconstrained integer convex optimization problem NP-hard?

Yes, since the shortest vector in lattice problem is NP-hard, see http://en.wikipedia.org/wiki/Lattice_problem
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4 votes

Maximizing positive definite quadratic using the eigendecompoisition

The reference where all is revealed is Bodlaender, Gritzman, Klee, Van Leeuwen
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5 votes

Computational complexity of finding the smallest number with n factors

The number of divisors of $n = \prod_{i=1}^k p_i^{\alpha_i}$ is $g(n)=\prod_{i=1}^k (1+\alpha_i)$ (your function differs from this by $2.$) So, once you have $g(n),$ you find the minimum over all fac …
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2 votes

Complexity of 2D-Minkowski sum of non-convex polygons

See Eli Fogel's slides. and be enlightened.
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7 votes

Can all convex optimization problems be solved in polynomial time using interior-point algor...

You should check out Boyd-Vanderberghe's convex optimization, available for free on Boyd's web page at Stanford. This has a discussion of the "easy" classes of convex optimization problems (google "se …
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