Sunday, 25 March 2007

ag.algebraic geometry - Nonsingular point on a hypersurface

Say we are given a hypersurface defined in variables textbfx=(x1,dotsxn)inmathbbRn given by P(textbfx)=0 for some homogeneous polynomial P, defined over mathbbR. I assume this is nondegenerate.



We are given a nonsingular point on this hypersurface textbfx0, say.



Question: Is it possible to find a point on the hypersurface arbitrarily close (Euclidean distance) to textbfx0 which is nonsingular with respect to a given subset of the variables? I.e. at least one of the partial derivatives from this subset is nonvanishing?



eg can we find an arbitrarily close point textbfx1 with fracpartialpartialxnP(textbfx)Big|textbfx=textbfx1neq0? Further could we even find a point arbitrarily close such that NONE of the partial derivatives vanish?

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