You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: clipping.m
    path of file: ./repos/MIMO_OFDM/第7章 PAPR/限幅和滤波
    
    the code of the file until where you have to start completion: function [x_clipped,sigma]=clipping(x,CL,sigma)
% CL   : Clipping Level
% sigma: sqrt(variance of x)

    
function [x_clipped,sigma]=clipping(x,CL,sigma)
% CL   : Clipping Level
% sigma: sqrt(variance of x)

%MIMO-OFDM Wireless Communications with MATLAB¢ç   Yong Soo Cho, Jaekwon Kim, Won Young Yang and Chung G. Kang
%2010 John Wiley & Sons (Asia) Pte Ltd

if nargin<3
  x_mean=mean(x); x_dev=x-x_mean; sigma=sqrt(x_dev*x_dev'/length(x));
end