# carrier.m

Returns the "carrier" Hamiltonian - the part of the Zeeman interaction Hamiltonian that corresponds to all particles having the Zeeman frequency prescribed by their free particle magnetogyric ratio and the magnet field specified by the user. This Hamiltonian is frequently used in rotating frame transformations.

## Syntax

    H=carrier(spin_system,spins)


## Arguments

    spins - a string specifying the isotope, e.g. '1H';
to select all spins, use 'all'.


## Outputs

    H - a Hamiltonian (Hilbert space) or its commutation
superoperator (Liouville space).


## Examples

Carrier Hamiltonians are used in rotating frame transformations (using rotframe.m) because they are normally the largest and the simplest (just a sum of Lz) part of any magnetic resonance Hamiltonian. Relevant calls may be seen in the source code of Spinach context functions (crystal.m, powder.m, singlerot.m, and others) as well as in the code of any functions that perform rotating frame transformations as a part of their housekeeping (e.g. fieldsweep.m and rapidscan.m).

## Notes

A carrier Hamiltonian is not the same as Zeeman Hamiltonian - it does not contain chemical shift or g-tensor information and should not therefore be used to create field gradient operators. To get the Zeeman part of the Hamiltonian, call hamiltonian.m with the corresponding option. For an example of how to do that see the source code of g2fplanck.m.