function V = build_alpert_matrix_2d(pos,k, options)

% build_alpert_matrix_2d - build 2D Alpert basis adapted to the sampling provided.
%
%   V = build_alpert_matrix_2d(pos,k);
%
%   The basis is hierarchical with respect to X direction ...
%
%   'pos' is a 2D vector, pos(:,i) is the ith point.
%   'k' is the number of vanishing moments (1=>Haar, 2=>linear basis ...).
%   'V' is an orthogonal matrix, each column is a basis vector.
%
%   Copyright (c) 2004 Gabriel Peyr