brob {Brobdingnag} R Documentation

## Brobdingnagian numbers

### Description

Create, coerce to or test for a Brobdingnagian object

### Usage

```brob(x = double(), positive)
as.brob(x)
is.brob(x)
```

### Arguments

 `x` Quantity to be tested, coerced in to Brobdingnagian form `positive` In function `brob()`, logical indicating whether the number is positive (actually, positive or zero)

### Details

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.

### Note

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.

### Author(s)

Robin K. S, Hankin

`glub`

### Examples

```
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)))

```

[Package Brobdingnag version 1.2-6 Index]