smdode45.m.

% function file for spring-mass-damper ode45 solution
%
function dydx = smdode45(time,variables)

m = 1;         % mass
c = 1;         % damping
k = 6;         % spring stiffness

t1 = 2;        % start time of square wave
t2 = 14;       % end time of square wave
fsquare = 10;  % square wave amplitude

if (time >= t1) & ( time <= t2)   % evaluate forcing function
  f = fsquare;                    % amplitude
else
  f = 0;
end

x = variables(1);                 % the input variables
v = variables(2);

dydx(1) = v;                      % and their derivatives
dydx(2) = (f - c*v - k*x)/m;