How to work with large numbers in R?
I would like to change the precision in a calculation of R. For example I would like to calculate x^6 with x = c(-2.5e+59, -5.6e+60). In order to calculate it I should change the precision in R, otherwise the result is Inf, and I don't know how to do it.
Answer
As Livius points out in his comment, this is an issue with R (and in fact, most programming language), with how numbers are represented in binary.
To work with extremely large/small floating point numbers, you can use the Rmpfr library:
install.packages("Rmpfr")
library("Rmpfr")
x <- c(-2.5e+59, -5.6e+60)
y <- mpfr(x, 6) # the second number is how many precision **bits** you want - NB: not decimal places!
y^6
# 2 'mpfr' numbers of precision 6 bits
# [1] 2.50e356 3.14e364
To work with numbers that are even larger than R can handle (e.g. exp(1800)) you can use the "Brobdingnag" package:
install.packages("Brobdingnag")
library("Brobdingnag")
## An example of a single number too large for R:
10^1000.7
# [1] Inf
## Now using the Brobdingnag package:
10^as.brob(1000.7)
# [1] +exp(2304.2)