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 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.