R how to add very small numbers

Question

It's probably easy, but I'm stuck on this small thing.

In R, I've being doing operations with likelihood values. Because they are very small I use their log representation to do their multiplication and division. However I need to add some now... how can I do that?

Example:

a and b are very small numbers

I have only A and B which are

A = ln a
B = ln b

How to compute

a + b

EDIT: I'm sorry for the unclear question. The answer is already present in Dealing with very small numbers in R

There is a formula for the sum of numbers represented by their log

@wolf_wue I did not understood your coment. I will edit the question for more clarification. — Diogo Santos, Sep 29 '17 at 08:30
Now it's much clearer, maybe consider about the inverse function of the natural logarithm, `exp()` — wolf_wue, Sep 29 '17 at 08:44

score 0 · Answer 1 · answered Sep 29 '17 at 08:42

I hope I got you right, but what I understood is that you want to compute

a+b

given that

A = ln a
B = ln b

holds.

To get a and b out of A and B you just need to apply the inverse function of the logarithm for an exponential basis, which is simply the expotential function:

a=exp(A)
b=exp(B)

R how to add very small numbers

1 Answers1