center2interval takes as argument a vector V of reals
and optionally a real as second argument
(by default V[0]-(V[1]-V[0])/2).
center2interval returns a vector of ranges of values having
the real values of the first argument as centers, where
the value of the second argument is
the left boundary of the first range.
Input :
Or (since the default value is 3-(5-3)/2=2) :
Output :
Input :
Output :