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: plotData.m
    path of file: ./repos/chebfun/@chebtech
    
    the code of the file until where you have to start completion: function data = plotData(f, g, h)
%PLOTDATA   Useful data values for plotting a CHEBTECH object.
%   DATA = PLOTDATA(F) returns a struct containing data that can be used for
%   plotting F. The struct DATA contains the following fields:
%
%       xLine: x-coordinates of for plotting smooth curves.
%       yLine: Function values of F at the coordinates stored in xLine.
%       xPoints: x-coordinates of the Chebyshev points used to represent F.
%       yPoints: Function value at the Chebyshev points used to represent F.
%   
%   DATA.xLine and DATA.yLine are used for plotting smooth curves (usually
%   passed to PLOT() with the '-' option). 
%
%   DATA.xPoints and DATA.yPoints contain the (x, F(x)) data at the Chebyshev
%   grid used to represent F, and are used for plots with marks (e.g.
%   PLOT(F,'-o').
%
%   DATA = PLOTDATA(F, G) is similar but for plot calls of the form PLOT(F, G),
%   where both F and G are CHEBTECH objects. 

    
function data = plotData(f, g, h)
%PLOTDATA   Useful data values for plotting a CHEBTECH object.
%   DATA = PLOTDATA(F) returns a struct containing data that can be used for
%   plotting F. The struct DATA contains the following fields:
%
%       xLine: x-coordinates of for plotting smooth curves.
%       yLine: Function values of F at the coordinates stored in xLine.
%       xPoints: x-coordinates of the Chebyshev points used to represent F.
%       yPoints: Function value at the Chebyshev points used to represent F.
%   
%   DATA.xLine and DATA.yLine are used for plotting smooth curves (usually
%   passed to PLOT() with the '-' option). 
%
%   DATA.xPoints and DATA.yPoints contain the (x, F(x)) data at the Chebyshev
%   grid used to represent F, and are used for plots with marks (e.g.
%   PLOT(F,'-o').
%
%   DATA = PLOTDATA(F, G) is similar but for plot calls of the form PLOT(F, G),
%   where both F and G are CHEBTECH objects. 
% 
%   DATA = PLOTDATA(F, G, H) is for plots of the form PLOT3(F, G, H). In this
%   instance, DATA also contains fields zLine and zPoints for the data
%   corresponding to H.
%
% See also PLOT.

% Copyright 2017 by The University of Oxford and The Chebfun Developers.
% See http://www.chebfun.org/ for Chebfun information.

if ( nargin == 1 )
    g = [];
end