Orthogonality

GUIDE: Mathematics of the Discrete Fourier Transform (DFT) - Julius O. Smith III. Orthogonality

NOTE: THIS DOCUMENT IS OBSOLETE, PLEASE CHECK THE NEW VERSION: "Mathematics of the Discrete Fourier Transform (DFT), with Audio Applications --- Second Edition", by Julius O. Smith III, W3K Publishing, 2007, ISBN 978-0-9745607-4-8. - Copyright © 2017-09-28 by Julius O. Smith III - Center for Computer Research in Music and Acoustics (CCRMA), Stanford University

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Orthogonality

The vectors (signals) $x$ and $y$ are said to be orthogonal if $\, denoted $x\. That is to say

\

Note that if $x$ and $y$ are real and orthogonal, the cosine of the angle between them is zero. In plane geometry ($N=2$), the angle between twoperpendicular lines is $\, and $\, as expected. More generally, orthogonality corresponds to the fact that two vectors in$N$-space intersect at a right angle and are thus perpendiculargeometrically.

Example ($N=2$):

Let $x=[1,1]$ and $y=[1,-1]$, as shown in Fig. 6.8.

Figure 6.8:Example of two orthogonal vectors for $N=2$.
\

The inner product is $\. This shows that the vectors are orthogonal. As marked in the figure, the lines intersect at a right angle and are therefore perpendicular.

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