If it ocillates, that means the mesh is not fine enough. Give it more passes. The delta is not some smooth function. It can get zero even at the second step by chance. n>The phase delay across boundaries along X-axis is set to 0?naha, that means a flat plane wave... or the next mode with 2pi...there's some uncertainty. Why would you need that? Leave it as ABC radiation, PML, or some symmetry boundary.n>Y-axis is assigned to a variable to be variednthat's how it is done when getting a dispersion curve.n