function xdot = triatom(x,t)
% Triatomic Euler and Green functions integration.
% Routine for integrating Euler's rigid body equations
% and Green's function for a triatomic molecule.  For
% ab initio IR spectra.  This appears to work.
% Use with either ode23 (better) or ode45.
%
% D. Holmgren holmgren@phobos.astro.uwo.ca

% moments of inertia for water molecule...
ixx = 1.720; iyy = 0.5766; izz = 1.1434;
% Euler's equations...
xdot(1) = -x(2) * x(3) * (izz - iyy) / ixx;
xdot(2) = -x(3) * x(1) * (ixx - izz) / iyy;
xdot(3) = -x(1) * x(2) * (iyy - ixx) / izz;
% Green's function matrix elements...
xdot(4) = x(2) * x(6) - x(3) * x(5);
xdot(5) = x(3) * x(4) - x(1) * x(6);
xdot(6) = x(3) * x(5) - x(2) * x(4);
xdot(7) = -x(3) * x(8) + x(2) * x(9);
xdot(8) = x(3) * x(7) - x(1) * x(9);
xdot(9) = -x(2) * x(7) + x(1) * x(8);
xdot(10) = -x(3) * x(11) + x(2) * x(12);
xdot(11) = x(3) * x(10) - x(1) * x(12);
xdot(12) = x(1) * x(12) - x(2) * x(10);