Improved Haar and Walsh functions over triangular domains

Piecewise constant orthogonal functions over triangular domains play an important role in many applications. In the present paper, some Haar and Walsh functions over triangular domains are constructed. Compared with the previously proposed Haar functions in [5], the new Haar functions take only integer. For any continuous function, the uniform convergence of the new Haar–Fourier series is proved. Moreover, based on the relation between the new Haar and Walsh functions, the uniform convergence of the Walsh–Fourier series is studied. Additionally, we obtain the relation between the Walsh functions in the two different orders, Paley order and Hadamard order, which have not been discussed previously.