Proving Entire Functions are Constant: f, e^f, Re f

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In summary, if an entire function is bounded, then e^f is also bounded, and if Re f is bounded, then f is constant. This can be proven using Liouville's theorem in complex analysis. The proof involves integrating the absolute value of the function, which can be simplified to show that the function must be constant.
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mathusers
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let f be an entire function..

1) prove if e^f is bounded then f is constant
2) prove that if Re f is bounded then f is constant

i'm guessing you would have to use suitable exponentials but i don't have a good enough idea of what to do here. any help would be greatly appreciated :Dxx
 
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You can start with if an entire function is bounded everywhere, it's constant.

http://en.wikipedia.org/wiki/Liouville's_theorem_(complex_analysis)

I think the proof moves the absolute value bars into the integral a bit prematurely (as generally a path integral of a real function can give a complex number as an answer, but I can't be bothered to check if in this case it actually comes out real all the time), but the basic idea is there
 

FAQ: Proving Entire Functions are Constant: f, e^f, Re f

What is an entire function?

An entire function is a complex-valued function that is analytic (differentiable) at every point in the complex plane.

How do you prove that an entire function is constant?

To prove that an entire function is constant, you can use Liouville's Theorem, which states that any bounded entire function must be constant. Alternatively, you can show that the function's derivative is identically zero, which also implies that the function is constant.

What is the significance of e^f in proving the constancy of an entire function?

e^f is important because it allows us to use the Cauchy-Riemann equations to show that the real and imaginary parts of an entire function are harmonic functions, which in turn helps us prove that the entire function is constant.

Can you give an example of a non-constant entire function?

Yes, one example is the function f(z) = z, which is an entire function that is not constant.

Is the converse true? If a function is not entire, does that mean it is not constant?

No, the converse is not always true. A function can be constant without being entire. For example, the function f(z) = 3 is a constant function that is not entire, since it is not analytic at any point other than z = 0.

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