On Tue, 15 Dec 2009, [email protected] wrote; (in part)
>
> x<-1:5
> y<-c(2.5,4.5)
> ks.test(x,y)
>
> The value of the D_2,5 statistic is calculated as 0.4 correctly, but the
> p-value is stated by R as 1, though in fact it should be 20/21=0.9524
What we seem to have here is a rounding error problem.
In ks.c:psmirnov2x, there is a double loop including
if(fabs(i / md - j / nd) > q)
u[j] = 0;
where md=2, nd=5, and q=3/10.
Now, to full precision abs(1/2 - 4/5) > 3/10 is false, but at least on my
MacBook it is true in C double precision.
I'm not sure why the loop is working with doubles, since multiplying by m*n
should make everything an integer.
-thomas
Thomas Lumley Assoc. Professor, Biostatistics
[email protected] University of Washington, Seattle
______________________________________________
[email protected] mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
