somewhere near the beginning.

1-forms and topology

Filed under: Mathematics — Alex @ 9:44 am 7/27/2007

I ended up not reading much algebraic topology on the way here (trying to wend your way through proofs on a bus, even ones that have already been worked out for you, turned out to be slow and unfruitful work), but I’ve started reading Fulton’s Algebraic Topology since I arrived.

One of the basic issues in algebraic topology seems to be the connection between integration (or more generally, any sort of analysis process) and the topology of a manifold. As an exemplar question: when can a given 1-form \omega = p(x,y) dx + q(x,y) dy be written as the differential of a function f, \omega = df?

I don’t know yet, and the suspense is killing me. In the meantime, here’s a problem: note that if f = \tan^{-1}(y/x) , then in the right half plane df = \frac{-y dx + x dy}{x^2 + y^2} . However, the one form \omega_\nu = \frac{-y dx + x dy}{x^2 + y^2} cannot be written as the differential of a function if the domain of definition is \R^2 \setminus (0,0). What if the domain of definition is the set
\{(re^t \cos(t), r e^t \sin(t)), 0<t&lt;4\pi, \frac{1}{2} < r < 2\}?

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