Handling A Failure to Couple

I may have found a good way to handle the failure to couple. It works like this:

1. Check whether or not coupling ocoured.
2. If so, proceed as normal
3. If not, skip making the forward chain and return a value of NULL

This should work for one and only one reason (at least with respect to the ABCIMA code) and that is because in R, we can append a NULL to a matrix and not change the matrix. Therefore, when the ABCIMA code gets a NULL back for a particular backward coupling instance, it will simply ignore it and try again as if nothing has happened.

As for how to handle this in the large scale numerical experiments, I’ll write a quick if-else which will map NULL values for the BCIMA result to a pair of NA’s for the point estimate and then this will make the distance NA and I can then both (1) count how many times BCIMA failed and (2) ignore the failures in the three-way comparison.