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Real algebraic geometry is the study of real solutions to algebraic equations with real coefficients. Its methods are rather different from classical algebraic geometry, which is typically done over an algebraically closed field (like the complex numbers).

45 votes
5 answers
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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 …
Noah Stein's user avatar
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14 votes
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Effective algorithm to test positivity

If by effective you mean "is this computable", then yes, the computational versions of Tarski-Seidenberg such as cylindrical algebraic decomposition give you a finite algorithm. (I suppose this is ass …
Noah Stein's user avatar
  • 8,501
1 vote

Hermitian forms with real coefficients

For $d=1$ this is true because $H(z)$ is a bilinear form on $\mathbb{R}^n$ and nonpositive definite by assumption, so it is of the form $H(z) = -\lVert Az\rVert^2$ for some real matrix $A$, and theref …
Noah Stein's user avatar
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