function f = Trig_Multi(A,g) %This is multiplication of hat_A*g, where hat_A is a tri-diag matrix, %with diag(hat_A) = A, and off diagnal = 1 [Nx,Nv,Nz_1,Nz_2] = size(A); g_plus = circshift(g,[0,-1,0,0]); g_plus(:,Nv,:,:) = zeros(Nx,1,Nz_1,Nz_2); g_minu = circshift(g,[0,1,0,0]); g_minu(:,1,:,:) = zeros(Nx,1,Nz_1,Nz_2); f = g_plus + A.*g + g_minu;