The NZD function I was using used .Machine$double.xmin for division
which limited the magnitude for minimum bandwidths (for categorical in
particular). I need better control of this so in order to get more
precise on lower bounds for the categorical bandwidths to, say
.Machine$double.eps, I need to adjust the NZD code... but in general
this might be a good thing... the NZD code is the industry standard
for testing for division by zero (if < 0 a, else b).