[R] Round error?

[Aurora Torrente]

Hi all,

I have tried to compute a p-value for a hypergeometric distribution as:

dhyper(x,k,l,n) + phyper(x,k,l,n,lower.tail=FALSE)

and sometimes obtained negative values.  Do you know if it is because a 
round error or am I doing something wrong?

Thanks in advance,

        Aurora