    def __generate_and_decompose_noise(self, j, state, params):
        """
        Generate and decompose the noise field into cascades for a given ensemble member.
        """
        eps = params["generate_noise"](
            params["pert_gen"],
            randstate=state["randgen_prec"][j],
            fft_method=state["fft_objs"][j],
            domain=params["domain"],
        )

        eps = params["decomp_method"](
            eps,
            params["filter"],
            fft_method=state["fft_objs"][j],
            input_domain=params["domain"],
            output_domain=params["domain"],
            compute_stats=True,
            normalize=True,
            compact_output=True,
        )

        return eps
Generate and decompose the noise field into cascades for a given ensemble member.
pysteps/nowcasts/steps.py