Overtone pa.m

Overtone soft pulse-acquire experiment. Syntax:

          spectrum=overtone_pa(spin_system,parameters,H,R,K)

where H is the hamiltonian commutation superoperator, R is the relaxation superoperator and K is the chemical kinetics superoperator. The following parameters are required:

   parameters.sweep           vector with two elements giving
                              the spectrum frequency extents
                              in Hz around the overtone frequency

   parameters.npoints         number of points in the spectrum

   parameters.rho0            initial state

   parameters.coil            detection state

   parameters.Lx
   parameters.Ly              X and Y Zeeman operators on the
                              quadrupolar nucleus

   parameters.rf_frq          pulse frequency offset from
                              the overtone frequency on the 
                              quadrupolar nucleus, Hz

   parameters.rf_pwr          pulse power on the quadrupolar 
                              nucleus, Hz

   parameters.rf_dur          pulse duration, seconds

   parameters.method          'average' uses the average Hamil-
                              tonian theory, 'fplanck' uses
                              Fokker-Planck formalism

Relaxation must be present in the system dynamics, or the matrix inversion operation below would fail to converge. The relaxation matrix should *not* be thermalized.