robot motion algorithm with classdef

i am creating an algorithm for robot motion with classdef that tries to reach goal point through the obstacles , the codes i wrote consisted with two parts , when i removed first one there is no error but if i run them together , there are many errros mainly

Illegal use of reserved keyword "classdef".

%first part
load("hw3007.mat");
a2=rot90(a);
imagesc(a2);
set(gca,'YDir','normal')
grid on
%second part
classdef Bug2 < Navigation
    properties(Access=protected)
        H       % hit points
        j       % number of hit points
        mline   % line from starting position to goal
        step    % state, in step 1 or step 2 of algorithm
        edge    % edge list
        k       % edge index
    end
    methods
        function bug = Bug2(varargin)
            %Bug2.Bug2 Construct a Bug2 navigation object 
            %
            % B = Bug2(MAP, OPTIONS) is a bug2 navigation object, and MAP is an occupancy grid,
            % a representation of a planar world as a matrix whose elements are 0 (free
            % space) or 1 (occupied).
            % 'goal',G      Specify the goal point (1x2)
            % 'inflate',K   Inflate all obstacles by K cells.
            bug = bug@Navigation(varargin{:});
            bug.H = [];
            bug.j = 1;
            bug.step = 1;
        end    
        function pp = query(bug, start, goal, varargin)
            %Bug2.query  Find a path
            %
            % B.query(START, GOAL, OPTIONS) is the path (Nx2) from START (1x2) to GOAL
            % (1x2).  Row are the coordinates of successive points along the path.  If
            % either START or GOAL is [] the grid map is displayed and the user is
            % prompted to select a point by clicking on the plot.            
            % - START and GOAL are given as X,Y coordinates in the grid map, not as
            %   MATLAB row and column coordinates.
            % - START and GOAL are tested to ensure they lie in free space.
            % - If the bug does a lot of back tracking it's hard to see the current
            %   position, use the 'current' option.
            % - For the movie option if M contains an extension a movie file with that
            %   extension is created.  Otherwise a folder will be created containing
            %   individual frames.
            bug.start = []; bug.goal = [];
            bug.checkquery(start, goal);
            % compute the m-line
            %  create homogeneous representation of the line
            %  line*[x y 1]' = 0
            bug.mline = homline(bug.start(1), bug.start(2), ...
                bug.goal(1), bug.goal(2));
            bug.mline = bug.mline / norm(bug.mline(1:2));
            
            % iterate using the next() method until we reach the goal
            robot = bug.start(:);
            bug.step = 1;
            path = bug.start(:);
                   
            % only return the path if required
            if nargout > 0
                pp = path';
            end
        end
        function plot_mline(bug, ls)          
                % parameters of the M-line, direct from initial position to goal
                % as a vector mline, such that [robot 1]*mline = 0
                
                if nargin < 2
                    ls = 'k--';
                end
                dims = axis;
                xmin = dims(1); xmax = dims(2);
                ymin = dims(3); ymax = dims(4);
                
                hold on
                if bug.mline(2) == 0
                    % handle the case that the line is vertical
                    plot([start(1) start(1)], [ymin ymax], 'k--');
                else
                    x = [xmin xmax]';
                    y = -[x [1;1]] * [bug.mline(1); bug.mline(3)] / bug.mline(2);
                    plot(x, y, ls);
                end
        end
        function n = next(bug, robot)            
            % implement the main state machine for bug2
            n = [];
            robot = robot(:);
            % these are coordinates (x,y)
          
            if bug.step == 1
                % Step 1.  Move along the M-line toward the goal

                if colnorm(bug.goal - robot) == 0 % are we there yet?
                    return
                end
                % motion on line toward goal
                d = bug.goal-robot;
                if abs(d(1)) > abs(d(2))
                    % line slope less than 45 deg
                    dx = sign(d(1));
                    L = bug.mline;
                    y = -( (robot(1)+dx)*L(1) + L(3) ) / L(2);
                    dy = round(y - robot(2));
                else
                    % line slope greater than 45 deg
                    dy = sign(d(2));
                    L = bug.mline;
                    x = -( (robot(2)+dy)*L(2) + L(3) ) / L(1);
                    dx = round(x - robot(1));
                end
                % detect if next step is an obstacle
                if bug.isoccupied(robot + [dx; dy])
                    bug.message('(%d,%d) obstacle!', n);
                    bug.H(bug.j,:) = robot; % define hit point
                    bug.step = 2;
                    % get a list of all the points around the obstacle
                    bug.edge = edgelist(bug.occgridnav == 0, robot);
                    bug.k = 2;  % skip the first edge point, we are already there
                else
                    n = robot + [dx; dy];
                end
            end % step 1

            if bug.step == 2
                % Step 2.  Move around the obstacle until we reach a point
                % on the M-line closer than when we started.
                if colnorm(bug.goal-robot) == 0 % are we there yet?
                    return
                end
                if bug.k <= numcols(bug.edge)
                    n = bug.edge(:,bug.k);  % next edge point
                else
                    % we are at the end of the list of edge points, we
                    % are back where we started.  Step 2.c test.
                    error('RTB:bug2:noplan', 'robot is trapped')
                    return;
                end
                % are we on the M-line now ?
                if abs( [robot' 1]*bug.mline') <= 0.5
                    bug.message('(%d,%d) moving along the M-line', n);
                    % are closer than when we encountered the obstacle?
                    if colnorm(robot-bug.goal) < colnorm(bug.H(bug.j,:)'-bug.goal)
                        % back to moving along the M-line
                        bug.j = bug.j + 1;
                        bug.step = 1;
                        return;
                    end
                end
                % no, keep going around
                bug.message('(%d,%d) keep moving around obstacle', n)
                bug.k = bug.k+1;
            end % step 2
        end % next
        function plan(bug)
            error('RTB:Bug2:badcall', 'This class has no plan method');
        end
    end % methods
end% classdef

Answer 1

[Maadhav Akula]

"classdef" is a reserved keyword used to define classes in MATLAB.

Only blank lines and comments can precede classdef. Hence you are getting that error. You have to define the second part (or) your class definitions in a seperate file. You can learn more about classdef and classes in MATLAB by referring the following links:

https://www.mathworks.com/help/matlab/ref/classdef.html

https://www.mathworks.com/help/matlab/object-oriented-programming.html

Hope this helps!