sounds like FAQ 7.31
Sent from my iPad
On Nov 7, 2013, at 18:39, Filippo <ingf...@gmail.com> wrote:
> Hi,
> I'm having strange differences between the R function prod ad the F90
> function product.
> Processing the same vector C (see attachment). I get 2 different results:
> prod(C) = 1.069678e-307
> testProduct(C) = 0
>
> where testProd is the following wrapping function:
>
> testProd <- function(x) {
> return(.Fortran('testProd', as.double(x), as.double(0), as.double(0),
> as.integer(length(x))))
> }
>
> subroutine testProd(x, p, q, n)
> implicit none
> integer, intent (in) :: n
> double precision, intent (in) :: x(n)
> double precision, intent (out) :: p
> double precision, intent (out) :: q
> integer :: i
>
> p = product(x)
> q=1
> do i = 1, n
> q = q*x(i)
> end do
> end subroutine testProd
>
> I check the lowest possible number and seems to be the same for both R and
> F90.
> Can anyone help me understanding this behaviour?
> Thank you in advance
> Regards,
> Filippo
>
> <C>
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