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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

45 votes
5 answers
9k views

Real algebraic geometry vs. algebraic geometry

This question is predicated on my understanding that real algebraic geometry (henceforth RAG) is the version of algebraic geometry (AG) one gets when replacing (esp. algebraically closed) fields with …
6 votes
Accepted

Analogue of PSD matrices for permanents?

The set $C$ is not convex, nor is its intersection with the symmetric matrices. To see this note that by linearly interpolating between each of the matrices below we maintain positive permanent and s …
Noah Stein's user avatar
  • 8,501
0 votes

Are there projective version of real Positivstellensatz?

If I understand correctly, you begin with a homogeneous $f$ of degree $2d$ (say), which is positive except at the origin. You would like a certificate that exhibits this positivity. If you dehomogen …
Noah Stein's user avatar
  • 8,501
4 votes
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Decide how many non-negative solutions a set of multivariate quadratic equations have

Not efficiently, at least not unless the problem has some additional structure which can be exploited. The set of mixed Nash equilibria of a two-player game can be written as the nonnegative solution …
Noah Stein's user avatar
  • 8,501