# Gridfree.m

Fokker-Planck magic angle spinning and SLE context. Generates a Liouvil- lian superoperator and passes it on to the pulse sequence function, which should be supplied as a handle. Syntax:

answer=fplanck(spin_system,pulse_sequence,parameters,assumptions)

where pulse sequence is a function handle to one of the pulse sequences located in the experiments directory, assumptions is a string that would be passed to assume.m when the Hamiltonian is built and parameters is a structure with the following subfields:

parameters.rate - spinning rate in Hz

parameters.axis - spinning axis, given as a normalized 3-element vector

parameters.spins - a cell array giving the spins that the pulse sequence involves, e.g. {'1H','13C'}

parameters.offset - a cell array giving transmitter off- sets in Hz on each of the spins listed in parameters.spins array

parameters.max_rank - maximum D-function rank to retain in the solution (increase till conver- gence is achieved, approximately equal to the number of spinning si- debands in the spectrum)

parameters.tau_c - correlation times (in seconds) for rotational dif- fusion under 'sle' option. Single number for iso- tropic rotational diffusion, two for axial and three for rhombic rotational diffusion. Other in- teractions and coordinates are assumed to be spe- cified in the rotational diffusion tensor eigenframe.

Additional subfields may be required by the pulse sequence. The parameters structure is passed to the pulse sequence with the following additional parameters set:

parameters.spc_dim - matrix dimension for the spatial dynamics subspace

parameters.spn_dim - matrix dimension for the spin dynamics subspace

This function returns the powder average of whatever it is that the pulse sequence returns.

Note: the choice of the Wigner function rank truncation level depends on the spinning rate (the slower the spinning, the greater ranks are required).

Note: rotational correlation times for SLE go into parameters.tau_c, not inter.tau_c (the latter is only used by the Redfield theory module).

Note: the state projector assumes a powder -- single crystal MAS is not currently supported.