Returns a finite difference representation of the Kuprov operator:
with the number of stencil points in the finite difference approximation specified by user. Syntax:
The following parameters are needed:
npoints - a three-element vector specifying the dimensions of the 3D cube of data that the operator will be acting on, in Angstroms.
chi - the electron magnetic susceptibility tensor in cubic Angstroms.
extents - a three-element vector specifying axis extents in Angstroms.
nstenc - number of finite-difference stencil points for the finite-difference approximations.
The resulting operator is a sparse matrix designed to act on the vectorization of rho. The dimensions of rho are assumed to be ordered as [X Y Z].
For further details see http://dx.doi.org/10.1039/C4CP03106G.