THEOREM 5 Theorem on Orthogonal Polynomials The sequence of polynomials defined inductively as follows is orthogonal: Pn(x) = (x-an) Pn-1(x) — bn Pn-2(x) (n ≥ 2) with po(x) = 1, p₁(x) = x − a₁, and an = (xPn-1, Pn-1)/(Pn-1, Pn-1) bn = (xPn-1, Pn-2)/(Pn-2, Pn-2)

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter3: Functions And Graphs
Section3.2: Graphs Of Equations
Problem 78E
Question

How do you find the legendre polynomial p3(x), p4(x), p5(x)?

**Legendre Polynomials Calculation**

To obtain the Legendre polynomials, we use Theorem 5 with the inner product defined as:

\[
\int_{-1}^{1} f(x)g(x) \, dx
\]

The initial steps in this calculation are as follows:

- \( p_0(x) = 1 \)

- Calculate \( a_1 \):

  \[
  a_1 = \frac{\langle p_0, p_0 \rangle}{\langle p_0, p_0 \rangle} = 0
  \]

- Define \( p_1(x) = x \)

- Calculate \( a_2 \):

  \[
  a_2 = \frac{\langle p_1, p_1 \rangle}{\langle p_1, p_1 \rangle} = 0
  \]

- Calculate \( b_2 \):

  \[
  b_2 = \frac{\langle p_1, p_0 \rangle}{\langle p_0, p_0 \rangle} = \frac{1}{3}
  \]

- Determine \( p_2(x) \):

  \[
  p_2(x) = x^2 - \frac{1}{3}
  \]

These calculations outline the process of deriving the first few Legendre polynomials using the specified inner product.
Transcribed Image Text:**Legendre Polynomials Calculation** To obtain the Legendre polynomials, we use Theorem 5 with the inner product defined as: \[ \int_{-1}^{1} f(x)g(x) \, dx \] The initial steps in this calculation are as follows: - \( p_0(x) = 1 \) - Calculate \( a_1 \): \[ a_1 = \frac{\langle p_0, p_0 \rangle}{\langle p_0, p_0 \rangle} = 0 \] - Define \( p_1(x) = x \) - Calculate \( a_2 \): \[ a_2 = \frac{\langle p_1, p_1 \rangle}{\langle p_1, p_1 \rangle} = 0 \] - Calculate \( b_2 \): \[ b_2 = \frac{\langle p_1, p_0 \rangle}{\langle p_0, p_0 \rangle} = \frac{1}{3} \] - Determine \( p_2(x) \): \[ p_2(x) = x^2 - \frac{1}{3} \] These calculations outline the process of deriving the first few Legendre polynomials using the specified inner product.
**Theorem 5: Theorem on Orthogonal Polynomials**

The sequence of polynomials defined inductively as follows is orthogonal:

\[ 
p_n(x) = (x - a_n)p_{n-1}(x) - b_n p_{n-2}(x) \quad (n \geq 2) 
\]

with \( p_0(x) = 1 \), \( p_1(x) = x - a_1 \), and

\[
a_n = \frac{\langle x p_{n-1}, p_{n-1} \rangle}{\langle p_{n-1}, p_{n-1} \rangle}
\]

\[
b_n = \frac{\langle x p_{n-1}, p_{n-2} \rangle}{\langle p_{n-2}, p_{n-2} \rangle}
\]

**Explanation:**

This theorem describes a method to build a sequence of orthogonal polynomials using an inductive approach. Starting with initial conditions \( p_0(x) \) and \( p_1(x) \), each subsequent polynomial \( p_n(x) \) is constructed based on its predecessors, minus terms involving coefficients \( a_n \) and \( b_n \). The orthogonality ensures that each polynomial in the sequence is distinct in its relation to others in terms of their polynomial spaces.
Transcribed Image Text:**Theorem 5: Theorem on Orthogonal Polynomials** The sequence of polynomials defined inductively as follows is orthogonal: \[ p_n(x) = (x - a_n)p_{n-1}(x) - b_n p_{n-2}(x) \quad (n \geq 2) \] with \( p_0(x) = 1 \), \( p_1(x) = x - a_1 \), and \[ a_n = \frac{\langle x p_{n-1}, p_{n-1} \rangle}{\langle p_{n-1}, p_{n-1} \rangle} \] \[ b_n = \frac{\langle x p_{n-1}, p_{n-2} \rangle}{\langle p_{n-2}, p_{n-2} \rangle} \] **Explanation:** This theorem describes a method to build a sequence of orthogonal polynomials using an inductive approach. Starting with initial conditions \( p_0(x) \) and \( p_1(x) \), each subsequent polynomial \( p_n(x) \) is constructed based on its predecessors, minus terms involving coefficients \( a_n \) and \( b_n \). The orthogonality ensures that each polynomial in the sequence is distinct in its relation to others in terms of their polynomial spaces.
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