fpt.zip_fast poisson_fast poisson matlab

function u = fpt(p, doInverse) % fpt -- Fast Poisson transform. % fpt(p) solves laplacian(u) = p, for matrix u, % assuming periodic boundary conditions. % fpt(p, doInverse) performs the inverse-transform % if "doInverse" is logically TRUE. % Copyright (C) 1998 Dr. Charles R. Denham, ZYDECO. % All Rights Reserved. % Disclosure without explicit written consent from the % copyright owner does not constitute publication. % Reference: Press, et al., Numerical Recipes, % Cambridge University Press, 1986 and later. % Version of 23-Oct-1998 09:02:58. if nargin < 1, help(mfilename), return, end if nargin < 2, doInverse = 0; end % Compute Fourier weights. [m, n] = size(p); i = (0:m-1).' * ones(1, n); j = ones(m, 1) * (0:n-1); weights = 2 * (cos(2*pi*i/m) + cos(2*pi*j/n) - 2); weights(1, 1) = 1; % Solve. if ~any(doInverse) u = ifft2(fft2(p) ./ weights); else u = ifft2(fft2(p) .* weights); end if isreal(p), u = real(u); end