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: m_shadedrelief.m
    path of file: ./repos/tracacode/1911-COAWST/script/mfiles/m_map
    
    the code of the file until where you have to start completion: function  [Truecol,x,y]=m_shadedrelief(x,y,Z,varargin)
% M_SHADEDRELIEF Shaded relief topography in an image
%  M_SHADEDRELIEF(X,Y,Z) presents a shaded relief topography, as would
%  be seen if a 3D model was artifically lit from the side. Slopes
%  facing the light are lightened, and slopes facing away from the 
%  light are darkened. X and Y are horizontal and vertical coordinate
%  VECTORS, and these should be in the same units as the height Z 
%  (e.g., all in meters), otherwise the slope angle calculations will be 
%  in error. 
%   
%  Usage notes:
%
%  (1) M_SHADEDRELIEF is a replacement for a low-level call to IMAGE 
%  displaying a true-colour image so it MUST be preceded by COLORMAP and 
%  CAXIS calls.  
%
%  (2) M_SHADEDRELIEF probably is most useful as a backdrop to maps with
%  a rectangular outline box - either a cylindrical projection, or some
%  other projection with M_PROJ(...'rectbox','on'). 
%
%  (3) Finally, the simplest way of not running into problems:

    
function  [Truecol,x,y]=m_shadedrelief(x,y,Z,varargin)
% M_SHADEDRELIEF Shaded relief topography in an image
%  M_SHADEDRELIEF(X,Y,Z) presents a shaded relief topography, as would
%  be seen if a 3D model was artifically lit from the side. Slopes
%  facing the light are lightened, and slopes facing away from the 
%  light are darkened. X and Y are horizontal and vertical coordinate
%  VECTORS, and these should be in the same units as the height Z 
%  (e.g., all in meters), otherwise the slope angle calculations will be 
%  in error. 
%   
%  Usage notes:
%
%  (1) M_SHADEDRELIEF is a replacement for a low-level call to IMAGE 
%  displaying a true-colour image so it MUST be preceded by COLORMAP and 
%  CAXIS calls.  
%
%  (2) M_SHADEDRELIEF probably is most useful as a backdrop to maps with
%  a rectangular outline box - either a cylindrical projection, or some
%  other projection with M_PROJ(...'rectbox','on'). 
%
%  (3) Finally, the simplest way of not running into problems:
%     - if your elevation data is in LAT/LON coords (i.e. in a matrix where
%       each row has points with the same latitude, and each column has points
%       with the same longitude), use 
%                  M_PROJ('equidistant cylindrical',...)
%     - if your elevation data is in UTM coords (meters E/N), i.e. in a matrix
%       where each row has the same UTM northing and the each column has the
%       same UTM easting, use
%                  M_PROJ('utm',....)
%
%  M_SHADEDRELIEF(...,'parameter',value) lets you set various properties.
%  These are:
%       'coords' : Coordinates of X/Y/Z: 
%                     'geog' for lat/lon, Z meters,  (default)
%                     'map'  for X/Y map coordinates, Z meters
%                     'Z' if X/Y/Z are all in same units (e.g., meters)
%       'lightangle' : true direction (degrees) of light source (default 
%                      -45, i.e. from the north-west)
%       'gradient': Shading effects increase with slope angle 
%                   until slopes reach this value (in degrees), and are 
%                   held constant for higher slopes (default 10). Reduce 
%                   for smoother surfaces.
%       'clipval' : Fractional change in shading for slopes>='gradient'.
%                  0 means no change, 1 means saturation to white or black
%                  if slope is facing directly towards or away from light 
%                  source, (default 0.9).
%       'nancol'  : RGB colour of NaN values (default [1 1 1]);
%       'lakecol' : RGB colour of lakes (flat sections) (default NaN)
%                   If set to NaN lakes are ignored.
%    
%   IM=M_SHADEDRELIEF(...) returns a handle to the image.
%
%   [SR,X,Y]=m_SHADEDRELIEF(...) does not create an image but only returns
%   the  true-color matrix SR of the shaded relief, as well as the X/Y
%   vectors needed to display it.
%
%   Example:
%           load topo
%           subplot(2,1,1);  % Example without it
%           imagesc(topolonlim,topolatlim,topo);
%           caxis([-5000 5000]);
%           colormap([m_colmap('water',64);m_colmap('gland',64)]);
%           set(gca,'ydir','normal');
% 
%           subplot(2,1,2);  % Example with it
%           caxis([-5000 5000]);
%           colormap([m_colmap('water',64);m_colmap('gland',64)]);
%           m_shadedrelief(topolonlim,topolatlim,topo,'gradient',5e2,'coord','Z');
%           axis tight
%

% Rich Pawlowicz (rich@eoas.ubc.ca) Dec/2017
%
% This software is provided "as is" without warranty of any kind. But
% it's mine, so you can't sell it.
%
% Changes:
% Jan/2018 - changed outputs for flexibility
%            and added 'map' coordinate handling
% Mar/2019 - added alphamapping for out-of-map areas, started using colormap
%            local to AXES not to FIGURE.
% Apr/2019 - some parts relied on the ones-expansion; went back to meshgrid
%            for compatibility with older matlab versions (thanks P. Grahn)

global MAP_PROJECTION MAP_VAR_LIST

lighthead=-45;
gradfac=10;
clipval=.9; 
nancol=[1 1 1];
lakecol=NaN; %[.7 .9 1];
geocoords='geog';
scfac=6400000;  % Used for geo coordinates if on sphere radius 1

while ~isempty(varargin)
    switch lower(varargin{1}(1:3))
        case 'coo'
            switch lower(varargin{2}(1))
                case 'g'
                    geocoords='geog';
                case 'm'
                    geocoords='map';
                case {'z','u'}
                    geocoords='z';
                otherwise
                    error('Unknown coordinate specification');
            end