[Rd] Non central chi squared bug (PR#9406)

[alan.bain at gmail.com]

Full_Name: Alan Bain 
Version: 2.4.0
OS: XP
Submission from: (NULL) (155.140.122.227)



Code for pnchisq contains following

if (tSml) {

if (x> f+ theta+ 5*sqrt(2*(f+2*theta) ))){
     return 1.; /* better than 0 --- but definately FIXME */
}

}

This needs to check which tail has been requested; it is only correct if the
default lower_tail=1 has been requested; for upper tail should return 0 if more
than 5 std devs away from mean under these circumstances.