function FF = poly_interp_per_2d( F , xx , L ) if nargin < 3 L = 2*pi; end xx = xx(:); N = size( F , 1 ); h = L/N; x = h*(1:N)'; Lsf = (2*pi)/L; Xd = xx*ones( 1 , length(x) ) - ones( length(xx) , 1 ) * x'; S = sin( Lsf*Xd*N*0.5 ) ./ ( N * ( tan( Lsf*Xd*0.5 ) ) ); S( Xd == 0 ) = 1; FF = S*F*(S');