[R] exact values for p-values

[Spencer Graves]

	  so my chi-square approximation was not very good:

 > pchisq(39540, 1, lower.tail=FALSE, log.p=TRUE)
[1] -19775.52
 > (pchisq(39540, 1, lower.tail=FALSE, log.p=TRUE)
+  /log(10))
[1] -8588.398

	  ... roughly 1e-8588.  With a few hours with Abramowitz and Stegun, I 
suspect I could do better.

	  spencer graves

David Duffy wrote:

>>This is obtained from F =39540 with df1 = 1, df2 = 7025.
>>Suppose am interested in exact value such as
>>
> 
> 
> If it were really necessary, you would have to move to multiple
> precision.  The gmp R package doesn't seem to yet cover this, but FMLIB
> (TOMS814, DM Smith) is a multiple precision f90 library that does
> include the incomplete beta -- it allows one to say for F(1,7025)=39540,
> P=6.31E-2886 (evaluated using 200 sign. digit arithmetic).  Results from
> R's pf() agree quite closely with the FMLIB results for less extreme values
> eg
> 
>>print(pf(1500,1,7025,lower=FALSE), digits=20)
> 
>  [1] 1.3702710894887480597e-297
> 
> cf   1.37027108948832580215549799419452388134616261215463681945E-297
> 
> 
> | David Duffy (MBBS PhD)                                         ,-_|\
> | email: davidD at qimr.edu.au  ph: INT+61+7+3362-0217 fax: -0101  /     *
> | Epidemiology Unit, Queensland Institute of Medical Research   \_,-._/
> | 300 Herston Rd, Brisbane, Queensland 4029, Australia  GPG 4D0B994A v
> 
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