Saturday, April 15, 2017

complex analysis - Analytic continuation of quotient of analytic functions




Suppose f(z) and g(z) are defined for some open subset U of the complex plane, and that they are holomorphic on that subset. We then know that their pointwise quotient (f/g)(z) is meromorphic on that subset.



Assume furthermore that both functions admit meromorphic continuations the entire complex plane, which I will denote as ˆf(z) and ˆg(z). Likewise, assume their pointwise quotient has a meromorphic continuation to the entire complex plane, denoted as ^(f/g)(z).



My question: if you analytically continue f and g separately, then take the quotient of the two functions, do you get the same thing as if you analytically continued (f/g) directly?



Or, expressed directly, do we have



ˆf(z)ˆg(z)=^(f/g)(z)




?


Answer



Yes, upon further thought, this is trivially true. If the functions ^f/g(z) and ˆf(z)ˆg(z) agree on some open subset U, then they have the same analytic continuation.


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