double(n=0) as.double(x) is.double(x)
double creates a double precision vector of the specified length.
Each element of the vector is equal to 0.
as.double attempts to coerce its argument to be of
double type.
is.double returns true or false
depending on whether its argument is of double type or not.
Note
R has no single precision data type.
All real numbers are stored in double precision format'.