6. Verify the orthogonality relation N-1 1 Σ e2nikn/Ne-2tiln/N N n=0 where Ski is the Kronecher's delta 1 {! 8kl = and Plancherel's identity = if k = 1 0 otherwise. Skl Hint: Write the exponential in terms of cosine and sine eix = cos(x) + i sin(x) when kl. Then use this orthogonality relation to prove Parceval's relation N-1 N-1 Σ f(n)g(n) = NΣ ƒ(k)ĝ(k) -NE n=0 k=0 N-1 N-1 Σ \f(n)|2 = N Σ \f(k)|2 n=0 k=0 for the discrete Fourier transform. Notice that Plancherel´s identity is a special case of Parceval's relation.

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### Orthogonality and Discrete Fourier Transform

This section will cover verifying orthogonality relations, and using this information to prove key identities in the discrete Fourier transform.

#### Verifying the Orthogonality Relation

The orthogonality relation is given by:

\[ 
\frac{1}{N} \sum_{n=0}^{N-1} e^{2\pi i kn/N} e^{-2\pi i ln/N} = \delta_{kl} 
\]

where \( \delta_{kl} \) is the Kronecker's delta, defined as:

\[
\delta_{kl} = 
\begin{cases} 
1 & \text{if } k = l \\
0 & \text{otherwise}
\end{cases}
\]

**Hint:** Write the exponential in terms of cosine and sine: \( e^{ix} = \cos(x) + i \sin(x) \), especially when \( k \neq l \).

#### Using Orthogonality to Prove Key Identities

Use the verified orthogonality relation to derive the following identities:

1. **Parseval's Relation**:

\[
\sum_{n=0}^{N-1} f(n) g(n) = N \sum_{k=0}^{N-1} \hat{f}(k) \hat{g}(k)
\]

2. **Plancherel's Identity**:

\[
\sum_{n=0}^{N-1} |f(n)|^2 = N \sum_{k=0}^{N-1} |\hat{f}(k)|^2
\]

for the discrete Fourier transform.

**Note:** Plancherel's identity is a special case of Parseval's relation where \( f = g \).
Transcribed Image Text:### Orthogonality and Discrete Fourier Transform This section will cover verifying orthogonality relations, and using this information to prove key identities in the discrete Fourier transform. #### Verifying the Orthogonality Relation The orthogonality relation is given by: \[ \frac{1}{N} \sum_{n=0}^{N-1} e^{2\pi i kn/N} e^{-2\pi i ln/N} = \delta_{kl} \] where \( \delta_{kl} \) is the Kronecker's delta, defined as: \[ \delta_{kl} = \begin{cases} 1 & \text{if } k = l \\ 0 & \text{otherwise} \end{cases} \] **Hint:** Write the exponential in terms of cosine and sine: \( e^{ix} = \cos(x) + i \sin(x) \), especially when \( k \neq l \). #### Using Orthogonality to Prove Key Identities Use the verified orthogonality relation to derive the following identities: 1. **Parseval's Relation**: \[ \sum_{n=0}^{N-1} f(n) g(n) = N \sum_{k=0}^{N-1} \hat{f}(k) \hat{g}(k) \] 2. **Plancherel's Identity**: \[ \sum_{n=0}^{N-1} |f(n)|^2 = N \sum_{k=0}^{N-1} |\hat{f}(k)|^2 \] for the discrete Fourier transform. **Note:** Plancherel's identity is a special case of Parseval's relation where \( f = g \).
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