Identical zero function in the complex plane

In summary, a holomorphic function in a region of the complex plane that is equal to zero inside a disk is also zero throughout the region. This is known as the Identity Theorem. Additionally, an entire function with uncountably-many zeros in the complex plane is also zero everywhere. This is because an entire function is determined by its power series coefficients. It is also possible to have a non-constant, continuous, even differentiable real-valued function with uncountably-many zeros. This is proven by using Weirstrass' theorem, which states that an uncountable subset of the plane must have a limit point in it. This is a corollary of the more fundamental result that a holomorphic function can be determined
  • #1
Silviu
624
11
Hi! If a holomorphic function ##f:G \to C##, where ##G## is a region in the complex plane is equal to zero for all values ##z## in a disk ##D_{[z_0,r]}##, inside ##G##, is it zero everywhere in the region G? And if this is true, does it mean that if an entire function is zero in a disk, it is zero in the whole complex plane? Thank you!
 
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  • #2
Yes, it is enough for f to be zero on a dense subset inside of the region G , i.e., a subset containing a limit point of G, in G. This is often called the Identity Theorem. EDIT: A related theorem is that the same holds for an entire function with uncountably-many zeros ( in the plane, of course, not extended-value).
 
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  • #3
I leave it as a challenge for you to find a Real-valued continuous, even differentiable non-constant function that has uncountably-many zeros.
 
  • #4
(as you know), even a countable convergent sequence of zeroes suffices to make a holomorphic function dead zero. the basic point is that an analytic entire function is determined by its power series coefficients, i.e. its derivatives at the center of the expansion, say at z = zero.
 
  • #5
mathwonk said:
(as you know), even a countable convergent sequence of zeroes suffices to make a holomorphic function dead zero. the basic point is that an analytic entire function is determined by its power series coefficients, i.e. its derivatives at the center of the expansion, say at z = zero.
Yes, I was using Weirstrass' theorem to show that an uncountable subset of the plane must have a limit point in it.
 
  • #6
thats why i mentioned the more fundamental result, since, as you say, yours is a corollary.
 

Related to Identical zero function in the complex plane

1. What is an identical zero function in the complex plane?

An identical zero function in the complex plane is a function that maps every complex number to zero, regardless of its input. It is a special case of a constant function, where the output is the same for all inputs.

2. How is an identical zero function different from a zero function?

An identical zero function is different from a zero function because it is defined to be zero for all inputs, while a zero function may have different outputs for different inputs.

3. What are the properties of an identical zero function?

Some properties of an identical zero function include being continuous, differentiable, and holomorphic (complex differentiable) everywhere in the complex plane. It also has a constant value of zero for all inputs.

4. What are some examples of an identical zero function?

The most common example of an identical zero function is the zero function itself, where the output is always zero for all inputs. Other examples include the function f(z) = 0, where z is a complex number, and the function g(z) = 0 + 0i, which is equivalent to the zero function.

5. What is the significance of the identical zero function in mathematics and science?

The identical zero function plays an important role in mathematics and science as it is used as a starting point for many mathematical proofs and serves as a building block for more complex functions. It also has applications in physics, engineering, and other fields where complex numbers are used to model and solve problems.

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