Interpreting ##\alpha \delta(x)##: Is ##\alpha## at ##x=0##?

  • Context: Graduate 
  • Thread starter Thread starter matematikuvol
  • Start date Start date
Click For Summary
SUMMARY

The discussion centers on the interpretation of the expression ##\alpha \delta(x)## in the context of Dirac delta functions. It establishes that while ##\delta(x)## is defined as ##\infty## at ##x=0## and ##0## elsewhere, interpreting ##\alpha \delta(x)## as having a value of ##\alpha## at ##x=0## leads to incorrect conclusions, specifically that $$\int \alpha\delta(x)dx=0$$, which contradicts the correct result of 1. The proper interpretation is that $$\alpha \cdot (+\infty) = +\infty$$ when ##\alpha > 0##, reinforcing that $$\int \alpha\delta(x)f(x)dx = \alpha f(0)$$ for any function f.

PREREQUISITES
  • Understanding of Dirac delta function properties
  • Familiarity with integral calculus
  • Knowledge of distribution theory
  • Basic grasp of mathematical limits and infinity
NEXT STEPS
  • Study the properties of the Dirac delta function in detail
  • Explore distribution theory and its applications in physics
  • Learn about the implications of infinity in calculus
  • Investigate the use of delta functions in signal processing
USEFUL FOR

Mathematicians, physicists, and engineering students who are working with distributions, delta functions, and integral calculus concepts.

matematikuvol
Messages
190
Reaction score
0
In Dirac definition ##\delta(x)## is ##\infty## when ##x=0##, and ##0## when ##x\neq 0##. My question is when I have some ##\alpha \delta(x)## could I interpret this like function which have value ##\alpha## in point ##x=0##?
 
Physics news on Phys.org
That interpretation would suggest that
$$\int \alpha\delta(x)=0$$ which is wrong. The right-hand side should be 1. Makes more sense to think of that value as ##\alpha\cdot(+\infty)=+\infty##, if ##\alpha>0##. Note that since
$$\int\delta(x)f(x)dx=f(0)$$ for all f, we should have
$$\int \alpha\delta(x)f(x)dx=\int\delta(x)(\alpha f)(x)dx =(\alpha f)(0)=\alpha f(0).$$
 

Similar threads

  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 21 ·
Replies
21
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 49 ·
2
Replies
49
Views
4K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K