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: fitMSD.m
    path of file: ./repos/msdanalyzer/@msdanalyzer
    
    the code of the file until where you have to start completion: function obj = fitMSD(obj, clip_factor)
%%FITMSD Fit all MSD curves by a linear function.
%
% obj = obj.fitMSD fits all MSD curves by a straight line

    
function obj = fitMSD(obj, clip_factor)
%%FITMSD Fit all MSD curves by a linear function.
%
% obj = obj.fitMSD fits all MSD curves by a straight line
%                      y = a * x + b.
% The fit is therefore rigorously valid only for purely
% diffusive behavior.
%
% Results are stored in the 'fit' field of the returned
% object. It is a structure with 2 fields:
% - a: all the values of the slope of the linear fit.
% - b: all the values for the intersect of the linear fit.
% - r2fit: the adjusted R2 value as a indicator of the goodness
% of the fit.
%
% obj = obj.fitMSD(clip_factor) does the fit, taking into
% account only the first potion of the average MSD curve
% specified by 'clip_factor' (a double between 0 and 1). If the
% value exceeds 1, then the clip factor is understood to be the
% maximal number of point to take into account in the fit. By
% default, it is set to 0.25.


if nargin < 2
    clip_factor = 0.25;
end