How to expand an analytical function on a given curve?

152 Views Asked by At

Since the Taylor expansion of a function that happens to have singularities for nearby values (including complex ones) does not globally converge, I am looking for a different way to expand a function that is analytical in a given interval $[a,b]$, or more generally, along a (finite) curve $\gamma:[0,1]\to\Gamma([0,1]) \subset \mathbb C$, that is valid for the whole interval/curve. Does such an expansion exist?

1

There are 1 best solutions below

1
On

I'm not sure what kind of expansion you are looking for. But for example, if the curve is simple (so that the complement of the curve is connected), Runge's theorem shows that $f$ can be written as a uniform limit (on the curve) of polynomials. In general though, there is no explicit fornula for the approximating polynomials.