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: lfsmooth.m
    path of file: ./repos/scGEAToolbox/+run/thirdparty/locfit/m
    
    the code of the file until where you have to start completion: function yhat = lfsmooth(varargin)
%
% a simple interface to locfit.
% output is a vector of smoothed values, at each data point.
% all locfit options, except evaluation structures, are valid.
%
% Example, to smooth a time series of observations,
%
% t = (1:100)';

    
function yhat = lfsmooth(varargin)
%
% a simple interface to locfit.
% output is a vector of smoothed values, at each data point.
% all locfit options, except evaluation structures, are valid.
%
% Example, to smooth a time series of observations,
%
% t = (1:100)';
% y = 2*sin(t/10) + normrnd(0,1,100,1);
% plot(t,y,'.');
% hold on;
% plot(t,lfsmooth(t,y,'nn',0.5));
% hold off;
%

% Minimal input validation
if nargin < 1
    error('At least one input argument required');
end