function[ikstarxf]=ikstar_back(dx,dy,ky,kx) %Forward Differencing on x ikstarxf=(-3+4*exp(i*kx*dx)-exp(2*i*kx*dx)/(2*dx); %Backward Differencing on x ikstarxb=(3-4*exp(-i*kx*dx)+exp(-2*i*kx*dx))/(2*dx); %Forward Differencing on y ikstaryf=(-3+4*exp(i*ky*dy)-exp(2*i*kx*dx))