Thursday, 12 November 2015

Complex Calculus question relating to Moreras theorem.



We have a ton of theorems for complex functions that are analytic on a domain D. We don't have very many iff statements in fact the one that i do have is stated as a totally different theorem.



Morera's theorem: let f be continuous on a domain D,



if Cf(z)dz=0 for every closed contour C in D then f is analytic throughout D.




I have found this theorem really useful for any well finite domain D is there some way we can apply this to say that for example f(z)=zc where zc is the complex conjugate (cant seem to figure out the bar language.)



i know that f(z)=zc is continuous on the complex plane if there some way to apply this theorem to show that it is not analytic on C?



I guess what im asking is like the converse of the principle of deformation of paths for f continuous true?


Answer



Let C={zC:|z|=1}. Then, since z¯z=1 for zC:



C¯zdz=C1zdz=2πi0


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