Create, coerce to or test for a Brobdingnagian object
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Quantity to be tested, coerced in to Brobdingnagian form
as.brob() is the user's workhorse: use this to coerce
numeric vectors to
is.brob() tests for its arguments being of class
brob() takes argument
x and returns a
formally equal to exp(x); set argument
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
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
brobs: objects of class
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
as.brob(1) + as.brob(c(1,NA)) returns an error.
Robin K. S, Hankin
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