# hcch_cosy.m

HCCH-COSY pulse sequence from Figure 7.26a of Protein NMR Spectroscopy (2nd edition) using the bidirectional propagation method described in (http://dx.doi.org/10.1016/j.jmr.2014.04.002). The sequence is hard-wired to work on 1H,13C proteins and uses PDB labels to select spins that will be affected by otherwise ideal pulses.

## Syntax

   fid=hcch_cosy(spin_system,parameters,H,R,K)


## Arguments

   parameters.npoints     - a vector of three integers giving the
number of points in the three temporal
dimensions, ordered as [t1 t2 t3].

parameters.sweep       - a vector of three real numbers giving
the sweep widths in the three frequen-
cy dimensions, ordered as [f1 f2 f3].

parameters.J_cc        - 13C-13C J-coupling to be used for mag-
netisation transfer, typically 35 Hz

parameters.J_ch        - 1H-13C J-coupling to be used for mag-
netisation transfer, typically 140 Hz

parameters.delta       - evolution delay, see the pulse sequence
diagram, typically 1.1e-3 seconds.

parameters.decouple_f3 - list of spins to be decoupled during
the detection period, typically {'13C'}

H   - Hamiltonian matrix, received from context function

R   - relaxation superoperator, received from context function

K   - kinetics superoperator, received from context function


## Outputs

   fid - three-dimensional free induction decay


## Examples

Below is the output of examples/nmr_proteins/hcch_cosy_gb1.m example file.

## Notes

1. Spin labels must be set to PDB atom IDs ('CA', 'HA', etc.) in sys.labels for this sequence to work properly.
2. F1 is 1H, F2 is C, F3 is H.