How to detect negative number in Switch and case statement

I want to implement some control actions based on the sign of the error and Uz.

when error = -1, Uz = -1.

The output is 'other value' instead of 'Object losing altitude'.

Please how can I correct it.

Thank you for the help.

error = -1;
Uz = -1;

    switch error
        case error > 0 && Uz > 0 
            disp('Controller should not take any action')
        case error > 0 && Uz < 0
            disp('Open the control valve and supply more lifting gas')
        case error < 0 && Uz < 0
            disp('Object losing altitude')
        otherwise
            disp('other value')
    end
    

Answer 1

[Scott MacKenzie]

Look carefully. Because you are switching on error, your first case expression reduces to

error == (error < 0 && Uz > 0)

which is false. In fact, all your case expressions are false so the otherwise statement always executes.

The fix: Just use an if-else arrangement:

error = -1;
Uz = -1;

if  error > 0 && Uz > 0
    disp('Controller should not take any action')
elseif error > 0 && Uz < 0
    disp('Open the control valve and supply more lifting gas')
elseif error < 0 && Uz < 0
    disp('Object losing altitude')
else
    disp('other value')
end

Object losing altitude

[Telema Harry]

Thank you for the feedback @Scott MacKenzie.

I was intentionally avoiding the if statement as I have up to 10 different conditions and the switch statement is easier to read. I will just stick with the if statement.

thanks for the help.