CODEWITHSUNDEEP
r
eric_kernfeld
eric_kernfeld

Reputation: 528

How can an R package produce a p-value with an exponent of -237?

I'm using the R package MAST and it produces some impressively small P-values -- so small I didn't think they could be stored as regular floating point values. Quadruple precision reaches only $10^{-34}$ (source). How is this possible?

Upvotes: 3

Views: 88

Answers (1)

grand_chat
grand_chat

Reputation: 541

This isn't just R; computers in general can store tiny numbers because floating point numbers are represented with a sign bit, a fraction, and an exponent. The space reserved for the exponent permits very large and very small numbers. See the R documentation on machine precision (noting e.g. the difference between double.eps and double.xmin), and the Wikipedia page on IEEE 754-1985 which describes the original standard for representing floating-point numbers (updated in 2008).

Upvotes: 4

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