Swapping the limits of integration

In summary, there are cases where you can swap the limits of integration and flip the sign of a one-dimensional integral, but it is not always true. This was brought up in the context of defining potential in electromagnetism, where the potential is defined as the negative of the integral with swapped limits. However, there may be situations where the positive integral with the original limits is equivalent. This may be why it is taught as a special case without being explicitly stated as such.
  • #1
Pythagorean
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Can you always just swap the limits of integration and flip the sign of a one-dimensional integral or is there a time when you can't do this?
 
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  • #2
Yes, [itex]\int_a^b f(x) dx= -\int_b^a f(x) dx[/itex]. Let u= -x. I thought everyone knew this!
 
  • #3
HallsofIvy said:
Yes, [itex]\int_a^b f(x) dx= -\int_b^a f(x) dx[/itex]. Let u= -x. I thought everyone knew this!

I was taught that yes... but it's not too uncommon to be taught something that's a special case without being told it's a special case.

The question came from the fact that in electromagnetism, we define the potential by the negative of the integral with swapped limits. I'm not sure why you would put the extra step in there if there wasn't a case where the positive with the limits restored wouldn't be equivalent.

My assumption (given your response) is that they do it simply because we generally define potential from some point at infinity down to a local point.
 

1. What is meant by "swapping the limits of integration"?

Swapping the limits of integration refers to the process of reversing the order in which the limits of an integral are written. This is done in order to make the integral easier to solve or to evaluate it from a different perspective.

2. Why would someone want to swap the limits of integration?

There are several reasons why someone might want to swap the limits of integration. One reason is to make the integral easier to solve, as it might be simpler to work with the new limits. Another reason is to change the perspective from which the integral is being evaluated, which can sometimes provide a different insight or understanding of the integral.

3. How do you swap the limits of integration?

The process of swapping the limits of integration is quite simple. All you need to do is reverse the order in which the limits are written. For example, if the integral is written as ∫ a to b, you would swap the limits to ∫ b to a.

4. Are there any restrictions on when you can swap the limits of integration?

Yes, there are some restrictions on when you can swap the limits of integration. One important restriction is that the integral must be convergent, meaning that it must have a finite value. Additionally, the integral must be able to be evaluated from both sets of limits, and the limits must be continuous at the point of swapping.

5. Can swapping the limits of integration change the value of the integral?

Yes, swapping the limits of integration can change the value of the integral. This is because the integral is being evaluated from a different perspective and may take into account different aspects or quantities. However, if the integral is convergent and the limits are continuous at the point of swapping, the value will remain the same.

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