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)