Solving Integral: Defining Branch Cut Prior

In summary, to solve the given integral, it is necessary to define a branch cut along the negative real axis and integrate along the real axis while avoiding the singularity at z=0. It may be helpful to work out the lower powers of log(x) before integrating log(x)^4.
  • #1
logmarie
6
0

Homework Statement


Define the branch cut prior to solving the following:
integrate from 0 to infinity of [log x]^4/ [1+x^2]


Homework Equations



The only poles inside the upper half plane is i

The Attempt at a Solution



How do I separate the countour?---help.

Thanks.
 
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  • #2
Just put a branch cut along the negative real axis. Now integrate along the real axis avoiding the singularity at z=0 with a little arc and closing in a big arc. I think you need to work out the lower powers of log(x) before you go direct to log(x)^4, but there may be a trick.
 

1. What is a branch cut in integral solving?

A branch cut is a mathematical concept used in complex analysis to define a discontinuity in a function. It is a line or curve on a complex plane where the function becomes undefined or multi-valued. In integral solving, branch cuts are important because they affect the path of integration and can change the value of the integral.

2. Why is it important to define a branch cut prior to solving an integral?

Defining a branch cut prior to solving an integral is important because it helps to avoid errors and inaccuracies in the solution. Without a defined branch cut, the path of integration may cross over the branch cut, resulting in a different value for the integral than intended. Defining a branch cut also helps to ensure that the integral has a well-defined solution.

3. How do you determine the location of a branch cut in an integral?

The location of a branch cut in an integral can be determined by analyzing the function and identifying where it becomes undefined or multi-valued. This can be done by looking for singularities, such as poles or branch points, in the function. The branch cut will typically extend from these singularities to the nearest other singularity or to infinity.

4. Can a branch cut be moved or altered in an integral?

Yes, a branch cut can be moved or altered in an integral, but this should only be done if absolutely necessary. Moving or altering a branch cut can change the value of the integral and may result in a different solution. It is important to carefully consider the effects of changing a branch cut before doing so.

5. Are there any techniques for simplifying the process of defining a branch cut?

Yes, there are some techniques that can be used to simplify the process of defining a branch cut in an integral. One approach is to use contour integration, which involves choosing a path of integration that avoids crossing over the branch cut. Another technique is to use Cauchy's residue theorem, which can help to identify the location and nature of singularities in the function.

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