How to handle large numbers?

Try Ryacas.  N means numerically evaluate in
yacas (as we don't want it evaluated on
the R side where we already know we get NaN).
library(Ryacas)
Eval(yacas("N(Exp(1000)/(Exp(1007)+5))")
[1] 0.000911882

You can explore it somewhat in R via:

 curve(exp(x)/(exp(x+7)+5), 1, 500)
Dear R,

I have two questions:

1, Why both R and Matlab give 0*Inf==NaN? To my knowledge, it should be zero
mathematically. Am I right?

2, I need to calculate e.g. exp(a)/(exp(b)+c), where both a and b are very
large numbers (>>1000, e.g a=1000, b=1007, and c=5). R gives me NaN when I
use the following command:

exp(1000)/(exp(1007)+5)
[1] NaN

I am pretty sure this should be close to zero. My question is whether there
is a general way to solve this kind of question or should I do some settings
before computing?

Thanks in advance!

Feng

--
Feng Li
Department of Statistics
Stockholm University
106 91 Stockholm, Sweden

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How to handle large numbers?

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