Laurent Expansion Problem (finding singularities)

In summary, the problem involves finding all Laurent expansions of the function f(z) = 1/(z(8(z^3)-1)) with centre z = 0. The attempt at a solution involved identifying the singularities at z = 0, z = 1/2, and z = (1/2)exp((n*pi*i)/3) where n = +-2,+-4,+-6... However, after considering the solution, it was realized that n can only be equal to 2 and 4. This is because n = 4 and n = -2 are equivalent, as well as n = -4 and n = 2. Additionally, n = 6 and n = 0
  • #1
Appledave
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0

Homework Statement


Find all Laurent expansion of the function f(z) = 1/(z(8(z^3)-1)) with centre z = 0.

The Attempt at a Solution



I tried to find all the singularities and came up with z = 0, z = 1/2, z = (1/2)exp((n*pi*i)/3)
where n = +-2,+-4,+-6... . But according to the solution n can only be 2 and 4, what am I missing?
 
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  • #2
n = 4 and n = -2 are the same (and n = -4 is the same as n = 2) n = 6 is the same as n = 0 which yields z = 1/2.
 
  • #3
exp((n*pi*i) = cos(n*pi) + i*sin(n*pi) = 1 + i*0 = 1 for n = +-2,+-4,+-6,+-8... isn't it? Wouldn't this make z = (1/2)exp((n*pi*i)/3) yield z = 1/2 for all n = +-2,+-4,+-6,+-8... ?
(making all n = +-2,+-4,+-6,+-8... equal, hence my confusion over why only n=2 and n=4 were included in the solution).
 
  • #4
There is a factor 1/3 in the exponential.
 
  • #5
But that factor disappears because you take z to the power of three in the function
[tex](f(z) = \frac{1}{z(8z^{3}-1)})[/tex]

Edit: nvm this post, I got it. thanks :)
 
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FAQ: Laurent Expansion Problem (finding singularities)

1. What is the Laurent Expansion Problem?

The Laurent Expansion Problem is a mathematical problem in complex analysis that involves finding the singularities of a function. Singularities are points in the complex plane where a function becomes infinite or undefined. The Laurent Expansion Problem is important in understanding the behavior of complex functions and is often used in physics and engineering applications.

2. How do you find singularities in a function?

To find the singularities of a function, you can use the Laurent Expansion formula, which expresses a complex function as a series of terms with different powers of a complex variable. The coefficients of these terms can help identify the singularities of the function. Another method is to plot the function on a complex plane and look for points where the function becomes infinite or undefined.

3. What is the difference between an isolated singularity and a non-isolated singularity?

An isolated singularity is a point where a function is undefined but can be made continuous by removing that point. On the other hand, a non-isolated singularity is a point where a function is undefined, and removing that point will not make the function continuous. In other words, a non-isolated singularity cannot be isolated or removed from the function.

4. Can a function have more than one singularity?

Yes, a function can have multiple singularities. These can be either isolated or non-isolated singularities, and they can be located at different points on the complex plane. The number and location of singularities can vary depending on the function and its properties.

5. Why is it important to find the singularities of a function?

Finding the singularities of a function is important because it helps us understand the behavior of the function. Singularities can indicate important points on the complex plane, such as poles or branch cuts, which can affect the convergence and accuracy of numerical calculations. Furthermore, the presence of singularities can give insight into the overall structure and properties of a complex function.

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