Returns: The sum of all the elements of the array.
If the array has length 1, returns the value of element 0.
Otherwise, the returned value is calculated by applying
operator+=
to a copy of an element of the array and
all other elements of the array in an unspecified order.
If the argument has the value −2,
the first two elements of the result will be value-initialized; the third element of the result will be assigned the value
of the first element of *this; etc.
Returns: A valarray of length size()
that is a circular shift of *this.
If element zero is taken as
the leftmost element, a non-negative value of n shifts
the elements circularly left n places and a negative
value of n shifts the elements circularly right −n places.