# correlation.m

Correlation order selection function - keeps only the specified orders of spin correlation in the state vector. This is useful as a replacement for gradients and phase cycles because correlation order filtering can be accomplished analytically, by just picking out the required correlation orders and zeroing everything else.

## Contents

## Syntax

rho=correlation(spin_system,rho,correlation_orders,spins)

## Arguments

rho - a state vector or a horizontal stack thereof orders - a row vector of correlation orders to keep spins - which spins to consider (e.g. '1H', '13C', 'all')

## Outputs

rho - the state vector with the undesired orders of spin correlations zeroed out

## Notes

Because quantum number information is required for this function to work, it is restricted to sphten-liouv formalism. It supports Fokker-Planck direct products.

## See also

coherence.m, decouple.m, homospoil.m

*Version 2.2, authors: Ilya Kuprov, Luke Edwards*