Questions tagged [legendre-polynomials]
For questions about Legendre polynomials, which are solutions to a particular differential equation that frequently arises in physics.
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Multidimensional Legendre polynomials?
Legendre polynomials can be given by several expressions, but perhaps the most compact way to represent them is by Rodrigues' formula as
$$P_n(x) = \frac{1}{2^n n!} \frac{d^n}{dx^n} (x^2 - 1)^n.$$
I ...
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Morse and Fesbach identity $\sum_{n=0}^{\infty} e^{-(n+\frac{1}{2})|u|} \; P_n(x) =(2\cosh u - 2x)^{-1/2}$
In book called Methods of theoretical physics from Morse and Feshbach, there is identity, which I wanted to prove ($P_n(x)$ are Legendre polynomials):
$$\sum_{n=0}^{\infty} e^{-(n+\frac{1}{2})|u|} \; ...
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Finding $l$ such that the Legendre differential equation has a polynomial solution
I was given this problem for practice and was wondering if my approach was correct:
$$
(1-x^2)y'' - 2xy' + 3ly = 0.
$$
At first I thought of just using $l = 2$ since the Legendre DE is defined in ...
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Is it possible to prove orthogonal form of integral of legendre polynomial solely from legendre's differential equation without using anything?
The differential equation for the Legendre polynomials
$P_n(x)$ is given by:
$(1 - x^2) \frac{d^2P_n}{dx^2} - 2x \frac{dP_n}{dx} + n(n + 1)P_n = 0$. Now I want to prove that $\begin{equation} \int_{-...
- 11
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Investigating the numerical accuracy of a truncated Legendre polynomial expansion of an unknown function
I have an integral equation involving an unknown function $f(x)$, of the most basic form
$$
\int_{-1}^{1} e^{iω(t) x} f(x) \ dx = g(t)
$$
I am solving for an approximation of $f(x)$ by substituting in ...
- 15
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Calculating the behaviour of an integral with Legendre polynomials of large order [closed]
I need to calculate the following integral:
$$\int_{\theta, \phi \in S^2} \left [ P_\ell(1-2\sin ^2\theta \sin^2\phi) \right ]^2 \sin\theta\, d\theta\, d\phi$$
where $S^2$ represents the unit sphere ...
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Closed Forms for Sums of Legendre Polynomials
I am investigating a series of the form $$\sum_{n=0}^\infty \frac{1}{1 + e^{nx}}P_n(x)$$ where $P_n$ is the Legendre Polynomial of degree $n$.
Because I am dealing with many of these series, it would ...
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legendre solution for non homogenous equation
given the legendre equation $(1-x^2)y'' - 2xy' + by = f(x)$
why can the solution be a series of legendre polynomials $y(x) = \sum_{n=0}^{\infty}a_n P_n(x)$? i thought legndre solves the homogenous ...
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How to express a Gaussian as a series of exponential? $\displaystyle e^{-x^2}=\sum_{n=1}^{\infty}c_n e^{-nx}$
Context
I would like to express the Gaussian function as a series of exponentials:
$$e^{-x^2}=\sum_{n=1}^{\infty}c_ne^{-n|x|}\qquad\forall x\in\mathbb{R}$$
For simplicity (the absolute value is added ...
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Expansion of $\frac{\text{erfc}({|\vec{r} - \vec{r'}|})}{|\vec{r} - \vec{r'}|}$ in spherical harmonics?
How can I derive the spherical harmonic expansion coefficients for the function $$ \frac{\text{erfc}({|\mathbf{r} - \mathbf{r'}|})}{{|\mathbf{r} - \mathbf{r'}|}} $$ by expressing it as $$f(\theta, \...
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Interpolation and general Gaussian quadrature
I just finished a course on numerical mathematics, and have become quite interested in interpolation and how it ties into numerical integration. What suprised me while studiyng quadrature was the fact ...
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Fourier-Legendre series for $x^n$
I'm struggling to find the Legendre expansion for $x^n$ (exercise 15.1.17 from Mathematical Methods for Physicists).
I'm trying to evaluate the following integral:
$$a_m = \frac{2m+1}{2} \int_{-1}^{1} ...
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Product of d-dimensional Legendre polynomials
Let $P_n:\mathbb{R}\rightarrow\mathbb{R}$ be the $d$-dimensional Legendre polynomials, that is they are orthonormal polynomials w.r.t the probability measure $\mu_d$ on $[-1,1]$ given by $\mu_d= \...
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How to caculate this integral by Legendre Poly.
How to caculate the integral
$$\int_{-1}^1(1-x^2)\mathrm{P}_k'(x)\mathrm{P}_l'(x)~\mathrm{d}x$$
Where $\mathrm{P}_l(x)$ is the $l$ - oeder Legendre Poly.
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Integral involving even order Legendre polynomials
Let $a>1$. We want to evaluate the integral
\begin{equation*}
\int_{-1}^1 \frac{P_{2n}(\xi)\,d\xi}{\sqrt{a^2-\xi^2}}
\end{equation*}
Mathematica is able to evaluate special cases for various $n$, ...
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