       auto_stiff logical = logical.empty;   % flag for computing stiffness coefficient automatically
        
        % Contact parameters
        stiff double = double.empty;   % stiffness coefficient
    end
    
    %% Constructor method
    methods
        function this = ContactForceT_Spring()
            this = this@ContactForceT(ContactForceT.SPRING);
            this = this.setDefaultProps();
        end
    end
    
    %% Public methods: implementation of super-class declarations
    methods
    