ndvar() gets and ndvar(n) sets the default number of
simulation in the 1D simulations or the number of simulation in the
variability dimension in the 2D simulations.
ndunc() gets and ndunc(n) sets the number of
simulations in the uncertainty dimension in the 2D simulations.
n is rounded to its ceiling value.
The default values when loaded are 1001 for ndvar and 101 for
ndunc.