[Bug-gsl] [Bug] gsl_cdf_tdist_P returns inaccurate p-value

[Lin, Kuan-Ting]

Hi all,

I am using gsl_cdf_tdist_P to get a p-value for the following two arrays:

x = 1, 2, 4, 2, 3, 1, 2, 4, 2, 1, 2
y = 11, 12, 13, 12, 13, 11, 14, 11, 12, 13, 12

(2* (1-gsl_cdf_tdist_P)) returns "8.882e-16”, but I got "9.189e-16” from 
t.test(x,y,var.equal=T) function in R (a statistics language). It suggests that 
gsl_cdf_tdist_P function is not returning a precise p-value.

In addition, I noticed that (2* (1-gsl_cdf_tdist_P)) doesn’t return double 
numbers. Instead, any p-value smaller than 1e-16 will be 0.

Could someone help me with this?

Thanks,
Woody