The default objective function used to determine convergence when fitting
a flash object. Calculates the difference in the
variational lower bound ("ELBO") from one iteration to the next.
flash_conv_crit_elbo_diff(curr, prev, k)The flash_fit object from the current iteration.
The flash_fit object from the previous iteration.
Only used during sequential backfits (that is, calls to
flash_backfit where extrapolate = FALSE). It then
takes the index of the factor/loadings pair currently being optimized.
A scalar, which is compared against the tolerance parameter
tol to determine whether a fit has converged.
This function is an example of a function that may be passed to
parameter fn in function flash_set_conv_crit to set
the convergence criterion for a flash pipeline. See
flash_set_conv_crit for details and examples.