Scaling functions on R2 for dilations of determinant ±2

This paper gives necessary and sufficient conditions for a doubly periodic function p(ξ), ξ∈R2 to be the squared modulus of a lowpass filter for a multiresolution analysis of L2(R2) with respect to an expanding matrix A of determinant ±2. By transferring the underlying spaces, R or R2, to a single binary sequence space, we are able to show that, when det(A)=2, every scaling function on R2 corresponds to one on R, where the dilation is ±2. If det(A)=−2, this is no longer true. In this case, the lowpass filter for the stretched Haar function makes an unexpected appearance.