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A general description is here.
The functions ‘.C()’, ‘.Call()’, ‘.External()’ and ‘.Fortran()’ now check that they are called with an unnamed first argument: the formal arguments were changed from ‘name=’ to ‘.NAME=’ in R 2.13.0, but some packages were still using the old name. This is currently a warning, but will be an error in future.
‘spline()’ and ‘splinefun()’ gain a new method ‘"hyman"’, an implementation of Hyman's method of constructing monotonic interpolation splines. (Contributed by Simon Wood and Rob Hyndman.)
‘arima.sim()’ could give too long an output in some corner cases (in part, PR#15068).