calculate_concentration: Building a proxy concentration matrix.
Description
If we don't have the true concentration matrix of the data rows calculated,
but at least have the $Z$ scores of individual rows, (unrealistically) assuming
independence and calculating the concentration matrix from those is still better
than nothing (i. e. the identity matrix).
Usage
calculate_concentration(data, Z.value)
Arguments
data
The data containing at least the expected values of $f$ statistics
(column D) and possibly also products of expected values and $f$
statistics divided by standard deviations of (the $Z$ scores,
column Z.value).
Z.value
Tells whether the $Z$ scores are available or should we just use the
identity matrix.
Value
The Cholesky decomposition of the inverted covariance matrix.