Êtes-vous un étudiant de l'EPFL à la recherche d'un projet de semestre?
Travaillez avec nous sur des projets en science des données et en visualisation, et déployez votre projet sous forme d'application sur GraphSearch.
Concept
Walsh matrix
Résumé
Hadamard matrix
In mathematics, a Walsh matrix is a specific square matrix of dimensions 2^n, where n is some particular natural number. The entries of the matrix are either +1 or −1 and its rows as well as columns are orthogonal, i.e. dot product is zero. The Walsh matrix was proposed by Joseph L. Walsh in 1923. Each row of a Walsh matrix corresponds to a Walsh function.
The Walsh matrices are a special case of Hadamard matrices. The naturally ordered Hadamard matrix is defined by the recursive formula below, and the sequency-ordered Hadamard matrix is formed by rearranging the rows so that the number of sign changes in a row is in increasing order. Confusingly, different sources refer to either matrix as the Walsh matrix.
The Walsh matrix (and Walsh functions) are used in computing the Walsh transform and have applications in the efficient implementation of certain signal processing operations.
The Hadamard matrices of dimension 2k for k ∈ N are given by the recursive formula (the lowest order of Hadamard matrix is 2):
and in general
for 2 ≤ k ∈ N, where ⊗ denotes the Kronecker product.
Rearrange the rows of the matrix according to the number of sign change of each row. For example, in
the successive rows have 0, 3, 1, and 2 sign changes. If we rearrange the rows in sequency ordering:
then the successive rows have 0, 1, 2, and 3 sign changes.
The sequency ordering of the rows of the Walsh matrix can be derived from the ordering of the Hadamard matrix by first applying the bit-reversal permutation and then the Gray-code permutation:
where the successive rows have 0, 1, 2, 3, 4, 5, 6, and 7 sign changes.
where the successive rows have 0, 1, 3, 2, 7, 6, 4, and 5 sign changes.
where the successive rows have 0, 7, 3, 4, 1, 6, 2, and 5 sign changes.
Source officielle
À propos de ce résultat
Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.