SD4 module performs spatial decorrelation of fourth order on the second order spatially whitened data
SD4 module attempts to resolve the intrinsic non-orthogonal dependencies in atomistic fluctuations. The second order projections from SD2 are used to build a fourth order spatially correlated cumulant tensor. SD4 approximately diagonalizes this tensor to return an anharmonic mode matrix.
Y - an mxT spatially whitened matrix (m dimensionality of subspace, T snapshots). May be a numpy array or a matrix where, m - dimensionality of the subspace we are interested in. Defaults to None, in which case m=n. T - number of snapshots of MD trajectory U - whitening matrix obtained after doing the PCA analysis on m components of real data verbose - print information on progress. Default is true.
W - a separating matrix for spatial decorrelation of order 4
SD4 implementation using pyANCA is done by making use of TD4 module and setting the lag parameter as zero (lag=0)