import torch


def omega_norm(Z, Omega):
    """
    Calculates norm(Omega * Z)

    :param Z: delta perturbation
    :param Omega: transformation matrix
    :return: l2 norm of delta multiplied by Omega
    """
    return torch.matmul(Omega, Z.view(Z.shape[0], -1).T).T.norm(dim=1)