[Rd] Bug in dt() function in stats - accuracy only 6 dp.

[mark.chappell]

Hi



I believe the dt() function in stats has small areas of inaccuracy.



SmallRangeMostDetaileddf150.png shows this occurring in the 10-11th decimal place.



MyD4 is computed using Myt_NC(), at the bottom of BugL.R - my function is very slow due to using mpfr, but i believe

accurate to the accuracy of genhypergeo() which it uses - 14-15 dp.



LargeRangeDiffdf150.png, which is difference between dt() and my function, shows spikes across -1.5 < x < 1.5.



I assumed probably only a problem for large df, but SmallRangeCloseZerodf20.png, shows actually more of a problem with

df = 20.  Accuracy seems to be only to 6 decimal places.



Using R version 3.5.2.



Cheers



Mark
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