y-derivative
for i = 1:nx for j = 1:ny
j2f[i,j] = 1.0im*wf[i,j]*ky[j]
j3f[i,j] = 1.0im*wf[i,j]*ky[j]/k2[i,j]
end~end
nxe = Int64(floor(nx*2/3))
nye = Int64(floor(ny*2/3))