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