This function is used in iterative NMF algorithms to manage variables
stored in a local workspace, that are accessible to all functions that
define the iterative schema described in NMFStrategyIterative-class.
It is specially useful for computing stopping criteria, which often require model data from different iterations.
staticVar(name, value, init = FALSE)
value is provided, that specifies
if the variable should be set to the new value only if it does not exist yet
(init=TRUE).The value of the static variable