SWITCH expression must be a scalar or a character vector. Error in pathplaninglaila (line 17) switch mode

% Parameters 
spacing = 10; % spiral spacing
delta_theta = pi/4; % spiral angle increment
pass_width = 10; % S-path pass width 

% Initialize position  
x = 0; 
y = 0;

% Initialize path mode
mode = 'random'; 

% Main loop
while true
    
    % Get next position based on mode
    switch mode
        case 'random'
            dx = rand*10 - 5; 
            dy = rand*10 - 5;
        
        case 'spiral'
            n = n+1;
            r = n*spacing;
            theta = n*delta_theta;
            dx = r*cos(theta);
            dy = r*sin(theta);
            
        case 's-path'
            if mod(y, pass_width)==0 
                dy = pass_width;
            else
                dy = -pass_width;
            end
            
        case 'wall follow'
            % Check sensors and turn if needed
            % ...
            dx = 1;
            
    end
    
    % Update position
    x = x + dx;
    y = y + dy;
    
    % Check for obstacles
    if obstacleDetected(x,y)
        % Backup and change path
        x = x - dx; 
        y = y - dy;
        mode = selectNewMode(); 
    end

    % Send motion commands
    moveTo(x,y);
    
    % Randomly change mode
    if rand < 0.1
        mode = selectNewMode();
    end
    
end

% Helper functions
function out = obstacleDetected(~,~)
  % Check map for obstacle at x,y
  out = false; 
end

function m = selectNewMode()
  % Pick random mode
  m = randsample({'random','spiral','s-path','wall follow'},1); 
end

function moveTo(x,y)
  % Send motion commands  
  disp(['Moving to ' num2str(x) ',' num2str(y)]);
end

Answer 1

[Dyuman Joshi]

As the error states, the switch expression is expected to be a scalar or character vector. In your case, you are dealing with text data, thus it should be a character vector.

Modify your function selectNewMode to provide the output as a character vector -

function m = selectNewMode()
  % Pick random mode
  m = randsample({'random','spiral','s-path','wall follow'},1); 
  m = m{:};
end

Note that you have not defined the variable n, to use it in the spiral case.

Also you have not put a break condition for the while loop.

And the function obstacleDetected paired with the if-else condition seems redundant.

Answer 2

[VBBV]

The mode variable used for the switch expression needs a character data type. you need to convert that variable to char mode as shown below. Some variables inside the switch-case statement are not defined and the while loop seems to run endlessly. Use a suitable while loop condition to stop the loop or break statements inside the loop.

% Parameters 
spacing = 10; % spiral spacing
delta_theta = pi/4; % spiral angle increment
pass_width = 10; % S-path pass width 

% Initialize position  
x = 0; 
y = 0;

% Initialize path mode
mode = 'random';
n = 0;  % initialize n

% Main loop
while true
    
    % Get next position based on mode
    switch mode
        case 'random'
            dx = rand*10 - 5; 
            dy = rand*10 - 5;
        
        case 'spiral'
            n = n+1;
            r = n*spacing;
            theta = n*delta_theta;
            dx = r*cos(theta);
            dy = r*sin(theta);
            
        case 's-path'
            if mod(y, pass_width)==0 
                dy = pass_width;
            else
                dy = -pass_width;
            end
            
        case 'wall follow'
            % Check sensors and turn if needed
            % ...
            dx = 1;
            
    end
    
    % Update position
    x = x + dx;
    y = y + dy;
    
    % Check for obstacles
    if obstacleDetected(x,y)
        % Backup and change path
        x = x - dx; 
        y = y - dy;
        mode = selectNewMode();
        mode = char(mode);  % convert it to char 
    end

    % Send motion commands
    moveTo(x,y);
    
    % Randomly change mode
    if rand < 0.1
        mode = selectNewMode();
        mode = char(mode); % convert to char         
    end
    
end

% Helper functions
function out = obstacleDetected(~,~)
  % Check map for obstacle at x,y
  out = false; 
end

function m = selectNewMode()
  % Pick random mode
  m = randsample({'random','spiral','s-path','wall follow'},1);
end

function moveTo(x,y)
  % Send motion commands  
  disp(['Moving to ' num2str(x) ',' num2str(y)]);
end