Symmetry of an Integral: Is it Zero?

  • Context: Graduate 
  • Thread starter Thread starter LagrangeEuler
  • Start date Start date
  • Tags Tags
    Integral Symmetry Zero
Click For Summary

Discussion Overview

The discussion revolves around the symmetry properties of integrals, specifically whether certain conditions on a function lead to the integral over a symmetric region being zero. Participants explore the implications of different symmetry conditions for both single and double integrals.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions if the integral ##\int^{a}_{-a}\int^{a}_{-a}f(x,y)dxdy## equals zero under the condition that ##f(-x,-y)=f(x,y)##.
  • Another participant counters with an example, stating that the integral of ##x^2 y^2## over the same limits does not yield zero, suggesting that the initial condition is not sufficient for the integral to be zero.
  • There is a request for clarification on why the zero result might only apply to one-dimensional integrals.
  • A participant notes that if a function satisfies ##f(-x,y) = -f(x,y)##, then the integral over the symmetric region should be zero, proposing that this condition is necessary.
  • Another participant revisits the original question, mistakenly thinking about the condition ##f(-x,-y)=-f(x,y)## and asks if this is always valid, while also questioning the validity of the condition ##f(-x,-y)=f(x,y)## leading to a specific relationship between the integrals.
  • A later reply outlines four cases for double integrals based on the symmetry of the function, indicating that different symmetry conditions lead to different implications for the integral's value.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the conditions under which the integral equals zero. Multiple competing views and interpretations of symmetry conditions remain present throughout the discussion.

Contextual Notes

Some participants express uncertainty regarding the applicability of symmetry conditions to both single and double integrals, and there are unresolved questions about the implications of different symmetry properties on the integral's value.

LagrangeEuler
Messages
711
Reaction score
22
If function is ##f(-x,-y)=f(x,y)##, is then

##\int^{a}_{-a}\int^{a}_{-a}f(x,y)dxdy=0##?
Thanks for answer.
 
Physics news on Phys.org
No, consider for example
$$\int_{-a}^a \int_{-a}^a x^2 y^2 \, dx dy$$
 
Could you tell me some explanation why this is valid only for one integral?
 
LagrangeEuler said:
Could you tell me some explanation why this is valid only for one integral?

The result does not hold for 1-dimensional integrals either. If f(x) = x2, then f(x) = f(-x) and integrating over any interval of the form [-a,a] (where a ≠ 0) gives you a non-zero number.

If you have a function that satisfies f(-x,y) = -f(x,y) then the integral over [-a,a] × [-a,a] should be zero. So you should probably look for a condition like this.
 
LagrangeEuler said:
If function is ##f(-x,-y)=f(x,y)##, is then

##\int^{a}_{-a}\int^{a}_{-a}f(x,y)dxdy=0##?
Thanks for answer.


Sorry I thought about ##f(-x,-y)=-f(x,y)##

Is it always valid?
Also is it valid in case ##f(-x,-y)=f(x,y)## that
##\int^{a}_{-a}\int^{a}_{-a}f(x,y)dxdy=2\int^{a}_{0}f(x,y)dxdy##
 
For double integrals there are four cases
f(x,y)
f(-x,y)
f(x,-y)
f(-x,-y)

f(-x,-y)=-f(x,y)
implies that
f(x,-y)=-f(x,-y)
thus
the integral would be zero

f(-x,-y)=f(x,y)
implies
f(-x,y)=f(x,-y)
##\int^{a}_{-a}\int^{a}_{-a}f(x,y)dxdy=2\int^{a}_{-a}\int^{a}_{0}f(x,y)dxdy##
 
Tnx.
 

Similar threads

  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 20 ·
Replies
20
Views
4K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 20 ·
Replies
20
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K