Fig. 4From: A novel high accuracy finite-difference time-domain methodPhase velocity errors in three dimensions: a in the entire wavenumber space; b at \((\theta ,\phi )=({0}^\circ ,{0}^\circ )\); c at \((\theta ,\phi )=({45}^\circ ,{0}^\circ )\); d \((\theta ,\phi )=({45}^\circ ,{45}^\circ )\)Back to article page