Integral depending on coordinate differences

In summary, the conversation discusses the possibility of simplifying a double integral by reducing it to a single integration using a change of variables. The suggested method is to use a change of variables like u=x-y, v=x+y, and then apply the Jacobian factor to the integral. This method is more efficient than trying to integrate the original double integral directly.
  • #1
Irid
207
1

Homework Statement


Consider a function which depends only on a difference between two variables, and integrate it with respect to both:
[tex]
\int_a^b \int_a^b f(x-y)\, dxdy
[/tex]
Is there any way to simplify this expression, like reducing it into a 1-D integral?
 
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  • #2
Irid said:

Homework Statement


Consider a function which depends only on a difference between two variables, and integrate it with respect to both:
[tex]
\int_a^b \int_a^b f(x-y)\, dxdy
[/tex]
Is there any way to simplify this expression, like reducing it into a 1-D integral?

Use a change of variables like u=x-y, v=x+y. That will reduce it to a single integration over u after you do the dv integration.
 
  • #3
This gives me
[tex] dxdy = (dv^2-du^2)/4 [/tex]
and I don't see how this makes the integral any easier
 
  • #4
Irid said:
This gives me
[tex] dxdy = (dv^2-du^2)/4 [/tex]
and I don't see how this makes the integral any easier

That's not how you do change of variables in double integration. dxdy is equal to dudv times a Jacobian factor, remember? http://en.wikipedia.org/wiki/Jacobian_matrix_and_determinant Then you have to change the limits.
 
  • #5
Oh, thanks Dick, I wasn't aware of this...
 

1. What is an integral depending on coordinate differences?

An integral depending on coordinate differences is a mathematical concept used in the field of multivariate calculus. It involves calculating the area under a curve or the volume under a surface by considering the differences in coordinates between two points.

2. How is an integral depending on coordinate differences different from a regular integral?

A regular integral calculates the area or volume by considering the entire region under the curve or surface. An integral depending on coordinate differences only takes into account the differences in coordinates between two points, making it a more precise and localized calculation.

3. What are the applications of integrals depending on coordinate differences?

Integrals depending on coordinate differences are commonly used in fields such as physics, engineering, and economics to calculate quantities such as work, force, and profit. They are also used in optimization problems and in the study of fluid dynamics.

4. What are the basic steps for solving an integral depending on coordinate differences?

The basic steps for solving an integral depending on coordinate differences are: 1) determining the limits of integration, 2) setting up the integral using the appropriate formula, 3) evaluating the integral using techniques such as substitution or integration by parts, and 4) interpreting the result in the context of the problem.

5. Are there any limitations to using integrals depending on coordinate differences?

One limitation of using integrals depending on coordinate differences is that they can only be applied to functions that are continuous and differentiable on the given interval. Additionally, they may not always provide an accurate representation of the entire region under the curve or surface, as they only consider the differences between two points.

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