# rotframe.m

Rotating frame transformation with respect to specified spins to specified order in perturbation theory (https://doi.org/10.1063/1.4928978).

## Syntax

    H=rotframe(spin_system,H0,H,isotope,order)


## Arguments

   H0     - carrier Hamiltonian with respect to which the
rotating frame transformation is to be done

H      - laboratory frame Hamiltonian H0+H1 that is to
be transformed into the rotating frame

isotope - string, such as '1H', specifying the spins
with respect to which the transformation is
being computed

order   - perturbation theory order in the rotating
frame transformation, this may be inf


## Outputs

   H       - rotating frame Hamiltonian


## Notes

The auxiliary matrix method is massively faster than either commutator series or diagonalisation.