# Slowpass.m

From Spinach Documentation Wiki

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 possibi- lity of getting spectrum values at specific frequencies without recalculating the entire free induction decay. Syntax:

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

where H is the Hamiltonian, R is the relaxation matrix and K is the chemical kinetics matrix.

The following parameters are required:

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

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