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This update changes one aspect of the default algorithm
for adaptive stratified sampling. Specifically it no longer
uses the same number of stratifications in each direction:
Mst+1 stratifications are used in the first D0 directions
and Mst in the remaining directions. This allows for more
hypercubes, which reduces errors and improves stability.
For many problems the difference is negligible, but
this change can lead to large improvements for high
dimensions or with a small number neval of integrand
evaluations. In particular there will always be some
stratification for arbitrarily high dimensions. The
default stratification is determined by neval and
new parameter neval_frac.
A related change is that AdaptiveMaps can now have
different numbers of increments in different directions.