pchisq increase decimal accurancy

Question

Is there any way to increase the decimal accuracy for probability distributions.

> 1-pchisq(90, 5)
[1] 0

But:

> pchisq(90, 5, lower.tail=F)
[1] 6.71932e-18

Answer 1

If you are doing the 1 - foo to get the upper tail of the distribution, then don't. Instead use the lower.tail argument:

> pchisq(90, 5, lower.tail = FALSE)
[1] 6.719319e-18