How do you integrate this function (not by parts)?

In summary, to integrate r2*exp(i*k*r - r2/a2) from -infinity to +infinity, you can complete the square in the exponential and change variables to y = r - b, where b is determined by completing the square. This will allow you to use known results for the integrals of Gaussian functions. Another possible substitution is z = r/a - \tfrac12 i a k, which can simplify the integral to terms of integrals like \int e^{z^2} and \int z e^{z^2}, which can be easily integrated without partial integration.
  • #1
zheng89120
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Homework Statement



integrate: r2*exp(i*k*r - r2/a2) from -infinity to +infinity (in terms of r)

Homework Equations



relevant integration table

The Attempt at a Solution



not sure what this function or the method to solve this function is called
 
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  • #2
I would start by completing the square in the exponential, and then changing variables to y = r - b, where b is whatever you get when you complete the square. Then, use know results for the integrals of Gaussian functions.
 
  • #3
Without going through the whole exercise, the thing that comes to mind is splitting off a square. I think that eventually you will find a substitution like [itex]z = r/a - \tfrac12 i a k [/itex] which will allow you to write it in terms of integrals like
[itex]\int e^{z^2}[/itex] and [itex]\int z e^{z^2}[/itex]
which you can do without partial integration.
 

1. How do you integrate a function without using the integration by parts method?

There are several methods for integrating a function without using the integration by parts method. One common method is substitution, where you substitute a new variable for a complicated part of the function and then use the chain rule to integrate. Another method is using trigonometric identities to simplify the function before integrating.

2. Can you explain the process of integrating a function without using the integration by parts method?

The process of integrating a function without using the integration by parts method involves identifying any patterns or relationships in the function that can be simplified or substituted. This may involve using trigonometric identities, algebraic manipulations, or other techniques. Once the function is simplified, it can then be integrated using traditional integration techniques.

3. How do you know when to use the integration by parts method?

The integration by parts method is most useful when the function to be integrated contains a product of two functions, or when the function contains a polynomial multiplied by an exponential function. In general, if the function cannot be simplified using other methods, the integration by parts method is a good option to try.

4. Can you provide an example of integrating a function without using the integration by parts method?

Sure, let's say we want to integrate the function f(x) = x^2 * e^x. Instead of using the integration by parts method, we can use the substitution method by letting u = x^2. This simplifies the function to u * e^x, which can then be integrated using the chain rule. The final result will be the same as if we had used the integration by parts method.

5. Are there any disadvantages to using the integration by parts method?

One potential disadvantage of using the integration by parts method is that it can be time-consuming and may require multiple iterations to find the correct combination of functions to integrate. Additionally, it may not always be applicable to every function, as some functions may not contain a product of two functions that can be integrated using this method.

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