Apply package mpfr for a function in R

Question

I want to apply package mpfr for a function as follows:

     f1  =function(x) exp(x)

if for example x = c(-1500, -2000, -6400, -7200)

     > x = c(-1500, -2000, -6400, -7200)
     >  mpfr(f1(x), precBits=64)
     4 'mpfr' numbers of precision  64   bits 
     [1] 0 0 0 0

I would like to get the values of function f1 even if its so small, how can I get it in R?

Answer 1

64 bits is not a whole lot. But primarily, you've made a mistake many of us did: the value of f1(x) is already zero because it's calculated before being converted into a bignum.

Try it this way:

> exp(mpfr(c(-1000,-5000),200))
2 'mpfr' numbers of precision  200   bits 
[1]  5.0759588975494567652918094795743369193055992828928373618323948e-435
[2] 3.3696941483089175144500323238132201679550979027292655581078801e-2172