From Spinach Documentation Wiki
Returns arbitrary-order central finite-difference differentiation matrix (sparse) with unit spacing and sided finite-difference schemes of the same order at the edges. Syntax:
dim - dimension of the column vector to be differentiated
npoints - number of points in the finite diffe- rence stencil
order - order of the derivative required
boundary - 'wall' fills the edges with sided finite difference schemes, 'pbc' assumes periodic boundaries. The default is 'wall'.