Struggling with Fourier Series Coefficient Integral for PDE Solution?

  • Thread starter Thread starter inko1nsiderat
  • Start date Start date
  • Tags Tags
    Integral
Click For Summary
SUMMARY

The discussion focuses on the calculation of Fourier series coefficients for a partial differential equation (PDE) using the integral an = (1/a) ∫ cos(nx) cos(x) dx over the interval -a to a. The orthogonality relations are critical, specifically ∫ cos(nx) cos(mx) dx = 0 for n ≠ m and π for n = m (where m ≠ 0) over the interval -π to π. The user initially applied these relations but encountered discrepancies when a is not equal to π, leading to the suggestion of using the Fundamental Theorem of Calculus (FTC) and consulting a table of integrals for antiderivatives. The discussion concludes that evaluating the integral correctly is essential for accurate coefficient determination.

PREREQUISITES
  • Understanding of Fourier series and their applications in PDEs.
  • Familiarity with orthogonality relations in trigonometric functions.
  • Knowledge of the Fundamental Theorem of Calculus (FTC).
  • Ability to use integral tables for finding antiderivatives.
NEXT STEPS
  • Study the properties of Fourier series in the context of PDE solutions.
  • Learn about the application of orthogonality relations in Fourier analysis.
  • Review the Fundamental Theorem of Calculus and its implications for integral evaluation.
  • Explore various integral tables and their use in solving Fourier series problems.
USEFUL FOR

Students and professionals in mathematics, particularly those studying Fourier analysis, PDEs, and integral calculus. This discussion is beneficial for anyone seeking to deepen their understanding of Fourier series coefficients and their computation.

inko1nsiderat
Messages
9
Reaction score
0

Homework Statement



The problem is in the solution to a PDE, the coefficient for the Fourier series is of some form like an=\frac{1}{a}\int cos(nx)cos(x) dx over the interval -a to a.

Homework Equations



Orthogonality relations:

\int cos(nx) cos(mx) dx =[ 0, n \neq m, pi n=m \neq 0

over the interval -pi to pi.

The Attempt at a Solution



Using the orthogonality relation I figured the answer would be 1/a*a for m=1, and 0 for n \neq m. However for a particular problem the book says there is a solution for n \neq m. Is there a better way to go about this particular integral?
 
Physics news on Phys.org
If a is not pi, then you can't use the orthogonality relation. This assumes your integral in step 1 is set up correctly. To evaluate it, just find the antiderivative and use FTC. Any decent table of integrals will have the antiderivative. There are two cases, n=1 and otherwise.
 
Billy Bob said:
If a is not pi, then you can't use the orthogonality relation. This assumes your integral in step 1 is set up correctly. To evaluate it, just find the antiderivative and use FTC. Any decent table of integrals will have the antiderivative. There are two cases, n=1 and otherwise.

Ah alright thanks very much.
 

Similar threads

Replies
1
Views
1K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
2
Views
1K
Replies
6
Views
2K
Replies
6
Views
1K