University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Orthogonal Functions and Fourier Series

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Vector Spaces Set of vectors Operations on vectors and scalars Vector addition: v 1 + v 2 = v 3 Scalar multiplication: s v 1 = v 2 Linear combinations: Closed under these operations Linear independence Basis Dimension

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Vector Spaces Pick a basis, order the vectors in it, then all vectors in the space can be represented as sequences of coordinates, i.e. coefficients of the basis vectors, in order. Example: Cartesian 3-space Basis: [i j k] Linear combination: xi + yj + zk Coordinate representation: [x y z]

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Functions as vectors Need a set of functions closed under linear combination, where Function addition is defined Scalar multiplication is defined Example: Quadratic polynomials Monomial (power) basis: [x 2 x 1] Linear combination: ax 2 + bx + c Coordinate representation: [a b c]

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Metric spaces Define a (distance) metric s.t. d is nonnegative d is symmetric Indiscernibles are identical The triangle inequality holds

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Normed spaces Define the length or norm of a vector Nonnegative Positive definite Symmetric The triangle inequality holds Banach spaces – normed spaces that are complete (no holes or missing points) Real numbers form a Banach space, but not rational numbers Euclidean n-space is Banach

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Norms and metrics Examples of norms: p norm: p=1 manhattan norm p=2 euclidean norm Metric from norm Norm from metric if d is homogeneous d is translation invariant then

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Inner product spaces Define [inner, scalar, dot] product s.t. For complex spaces: Induces a norm:

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Some inner products Multiplication in R Dot product in Euclidean n-space For real functions over domain [a,b] For complex functions over domain [a,b] Can add nonnegative weight function

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Hilbert Space An inner product space that is complete wrt the induced norm is called a Hilbert space Infinite dimensional Euclidean space Inner product defines distances and angles Subset of Banach spaces

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Orthogonality Two vectors v 1 and v 2 are orthogonal if v 1 and v 2 are orthonormal if they are orthogonal and Orthonormal set of vectors (Kronecker delta)

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Examples Linear polynomials over [-1,1] (orthogonal) B 0 (x) = 1, B 1 (x) = x Is x 2 orthogonal to these? Is orthogonal to them? (Legendre)

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Fourier series Cosine series

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Fourier series Sine series

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Fourier series Complete series Basis functions are orthogonal but not orthonormal Can obtain a n and b n by projection

University of Texas at Austin CS395T - Advanced Image Synthesis Spring 2006 Don Fussell Fourier series Similarly for b k