# slowpass.m

Slow passage detection - calculates spectrum values at the user specified frequency positions using the Fourier transform of the Liouville - von Neumann equation. The biggest advantage over the fid+fft style detection is easy parallelization and the possibility of getting spectrum values at specific frequencies without recalculating the entire free induction decay.

## Syntax

spectrum=slowpass(spin_system,parameters,H,R,K)

## Arguments

parameters.sweep vector with two elements giving the spectrum frequency extents in Hz parameters.npoints number of points in the spectrum parameters.rho0 initial state parameters.coil detection state H - Hamiltonian matrix, received from context function R - relaxation superoperator, received from context function K - kinetics superoperator, received from context function

## Outputs

spectrum - the spectrum of the system with the specified starting state detected on the specified coil state within the frequency interval requested

## Examples

The 14N overtone MAS spectrum of glycine recorded using this method (examples/nmr_overtone/mas_glycine_1.m) appears below. FID+FFT simulation in this system is much slower.

## Notes

Relaxation must be present in the system dynamics, or the matrix inversion operation would fail to converge. The relaxation matrix R should *not* be thermalized.

## See also

acquire.m, fieldscan_enlev.m, fieldscan_magn.m, fieldsweep.m, rapidscan.m

*Version 2.3, authors: Ilya Kuprov*