Deer 4p soft deer.m

Four-pulse DEER/PELDOR pulse sequence. The sequence uses soft pulses computed with the Fokker-Planck formalism. Syntax:

     deer=deer_4p_soft_deer(spin_system,parameters,H,R,K)

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

     parameters.pulse_frq  - frequencies for the 
                             four pulses, Hz

     parameters.pulse_pwr  - power levels for the four
                             pulses, Hz

     parameters.pulse_dur  - durations for the four
                             pulses, seconds

     parameters.pulse_phi  - initial phases for the four 
                             pulses, radians

     parameters.pulse_rnk  - Fokker-Planck ranks for the
                             four pulses

     parameters.p1_p2_gap  - time between the end of the 
                             first and the start of the
                             second pulse, seconds

     parameters.p2_p4_gap  - time between the end of the 
                             second the start of the third
                             pulse, seconds

     parameters.p3_nsteps  - number of third pulse posi-
                             tions in the interval between
                             the first echo and the fourth
                             pulse

     parameters.echo_time  - time to sample around the ex-
                             pected second echo position

     parameters.echo_npts  - number of points in the second
                             echo discretization

     parameters.rho0       - initial state

     parameters.coil       - detection state

     parameters.method     - soft puse propagation method,
                             'expv' for Krylov propagation,
                             'expm' for exponential propa-
                             gation, 'evolution' for Spin-
                             ach evolution function