function dx=R(t,x);
% Compound pendulum
dx = zeros(2,1);  % a column vector
W=12; L=3; g=32.2; m=W/g;
dx(1) = x(2);
dx(2) =  -3*g*cos(x(1))/(2*L);

% dx=[ x(2) ; -3*g*cos(x(1))/(2*L) ];