Discretization of 2D and 3D wave spectrum

Hello all,

I need your help!!! I am trying to generate water surface elevations considering 2D and 3D seas. For this I need to discretize e.g. Pierson-Moskowitz spectrum into N equal area segments (relative amplitudes). However, I cannot think of a way how to perform discretization of the spectras. Can someone give any tips or maybe give an example as a Matlab code? I really need help as I am very new at using Matlab.

Thanks in advance for any help!