function [t, y] = SMDSF(k, m, w, e, ti, tf)     % ‘SDSF’ for ‘Spring-Mass-Damper Stationary Frame’

% [t, y] = SDSFpar(104000,1/16,1,1,0,1000)

% Physical Parameters

M = 200;
C = 10;

% Initial Conditions

initialX = 0.0;
initialVx = 0;
initialY = 0;
initialVy = 0;

% Tolerances

tol = odeset('RelTol', 1e-8, 'AbsTol', 1e-9);

%     initial X, initial X', initial Y, initial Y'
ic = [initialX; initialVx; initialY; initialVy];
tspan = [ti tf];

% Equations of motion
% y(1) = X1
% y(2) = X2 = X1'
% y(3) = Y1
% y(4) = Y2 = Y1'

[t,y] = ode45(@odefun, tspan, ic, tol);

    function dydt = odefun(t,y)
        %SDOF (Uncoupled) Forced (Unbalance), Undamped
        
        dydt = zeros(2,1);
        dydt(1) = y(2);
        dydt(2) = -(k/M)*y(1)+(m/M)*e*w^2*cos(w*t)-(C/M)*y(2);
        dydt(3) = y(4);
        dydt(4) = -(k/M)*y(3)+(m/M)*e*w^2*sin(w*t)-(C/M)*y(4);
              
    end
        
        
%hold all
%plot(t,y(:,1),'-or')
%plot(t,y(:,3),'-ob')
%plot(t,(y(:,1).*y(:,1)+y(:,3).*y(:,3)).^0.5,'-og')

end