Legendre Polynomials & the Generating function

In summary, the conversation is discussing the solution to a problem involving Legendre polynomials in chapter 1. It is mentioned that P[2n+1](0) = 0 is always true for odd Legendre polynomials, but the speaker is unsure how to prove this using the Generating function. The second part of the question involves equating two expressions, and the speaker is unsure how to approach it. They mention expanding one expression as a Maclaurin series, but are unsure how to proceed from there.
  • #1
dykuma
56
7

Homework Statement


upload_2016-11-3_23-24-38.png

Homework Equations


upload_2016-11-3_23-24-49.png

and in chapter 1 I believe that wanted me to note that
upload_2016-11-3_23-35-14.png

The Attempt at a Solution


For the first part of this question, as a general statement, I know that P[2 n + 1](0) = 0 will be true as 2n+1 is an odd number, meaning that L is odd, and so the Legendre polynomial will be odd. With odd Legendre polynomials, every coefficient has a term of x attributed to it (example P3(x) = 1/2(5x^3 - 3x)), so if it were to be evaluated at 0, the result will always be zero. However I am not sure how to prove that using the Generating function.

As for the second part of this question, I am not really sure what to do. For now I am looking for a place to start with that.

[EDIT] I did expand 5.1 as a Maclaurin Series, but I don't see how they want me to equate that to 5.2.
 

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  • #3
I figured out the solution, just posting it here for sake of completeness.

upload_2016-11-13_21-29-28.png
 

What are Legendre polynomials?

Legendre polynomials are a set of orthogonal polynomials named after French mathematician Adrien-Marie Legendre. They are commonly used in mathematical physics and engineering, and have applications in solving differential equations and approximating functions.

What is the generating function for Legendre polynomials?

The generating function for Legendre polynomials is given by (1-x^2)^{-1/2} = \sum_{n=0}^\infty P_n(x)t^n where P_n(x) is the n-th Legendre polynomial. This function allows for the convenient computation of Legendre polynomials.

How are Legendre polynomials related to spherical harmonics?

Legendre polynomials are closely related to spherical harmonics, which are functions used to describe the solutions of Laplace's equation in spherical coordinates. The Legendre polynomials P_n(x) can be used to construct spherical harmonics Y_n^m(\theta, \phi) as Y_n^m(\theta, \phi) = P_n^m(\cos\theta)e^{im\phi}, where m is an integer representing the azimuthal quantum number.

What is the recurrence relation for Legendre polynomials?

The recurrence relation for Legendre polynomials is given by nP_n(x) = (2n-1)xP_{n-1}(x) - (n-1)P_{n-2}(x) for n>1. This relation allows for the efficient computation of Legendre polynomials of higher degree using those of lower degree.

Can Legendre polynomials be used to approximate any function?

Yes, Legendre polynomials can be used to approximate any continuous function on the interval [-1, 1]. This is because they form a complete orthogonal system, meaning that any continuous function can be approximated by a linear combination of Legendre polynomials. However, the accuracy of the approximation depends on the number of terms used in the linear combination.

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