brob {Brobdingnag} | R Documentation |
Create, coerce to or test for a Brobdingnagian object
brob(x = double(), positive) as.brob(x) is.brob(x)
x |
Quantity to be tested, coerced in to Brobdingnagian form |
positive |
In function |
Function as.brob()
is the user's workhorse: use this to coerce
numeric vectors to brob
s.
Function is.brob()
tests for its arguments being of class
brob
.
Function brob()
takes argument x
and returns a brob
formally equal to exp(x); set argument positive
to
FALSE
to return -exp(x). Thus calling function
exp(x)
simply returns brob(x)
. This function is not
really intended for the end user: it is confusing and includes no
argument checking. In general numerical work, use function
as.brob()
instead, although be aware that if you really really
want e^1e7, you should use brob(1e7)
;
this would be an exact representation.
Real numbers are represented by two objects: a real, holding the logarithm of their absolute values; and a logical, indicating the sign. Multiplication and exponentiation are easy: the challenge is addition. This is achieved using the (trivial) identity log(e^x+e^y)=x+log(1+e^(y-x)) where, WLOG, y<x.
Complex numbers are stored as a pair of brob
s: objects of class
glub
.
The package is a simple example of S4 methods. However, it could be viewed as a cautionary tale: the underlying R concepts are easy yet the S4 implementation is long and difficult. I would not recommend using S4 methods for a package as simple as this; S3 methods would have been perfectly adequate. I would suggest that S4 methods should only be used when S3 methods are demonstrably inadequate.
The package has poor handling of NA
and NaN
. Currently,
as.brob(1) + as.brob(c(1,NA))
returns an error.
Robin K. S, Hankin
googol <- as.brob(10)^100 googolplex <- 10^googol (googolplex/googol) / googolplex # Thus googolplex/googol == googolplex (!) # use cbrob() instead of c() when Brobdingnagian numbers are involved: cbrob(4,exp(as.brob(1e55)))