contrastiveCov: Contrastive Covariance Matrices
In scPCA: Sparse Contrastive Principal Component Analysis

Compute the list of contrastive covariance matrices.

1	contrastiveCov(target, background, contrasts, center, scale)

`target`	The target (experimental) data set, in a standard format such as a `data.frame` or `matrix`.
`background`	The background data set, in a standard format such as a `data.frame` or `matrix`.
`contrasts`	A `numeric` vector of the contrastive parameters.
`center`	A `logical` indicating whether the target and background data sets should be centered to mean zero.
`scale`	A `logical` indicating whether the target and background data sets should be scaled to unit variance.