Fri 19 Sep 2014 04:20:37 PM UTC, original submission:
From zoudm =at= pku =dot= edu =dot= cn
Hello,
I’m testing about floating point accuracy, and I have found that 9 functions in specfunc have potential bugs of inaccuracy.
I’m using gsl1.1.6 in Ubuntu 64bit.
Below is the inputs. To make the inputs precise, I encode them in hexadecimal.
double i2d(unsigned long int x) {
double d = (double)(&x);
return d;
}
gsl_sf_hyperg_0F1(i2d(0x13675FCCC1DE0AE1), i2d(0xDD0DD58CDBC5592)) with estimate of the absolute error(result>err, the same below) is 6.501089E+185, but actual absolute error is 1.149822E+198.
gsl_sf_hyperg_0F1(i2d(0x19A2961396A4C4D0), i2d(0x19A2961396A4C4D0)) with estimate of the absolute error is 5.877511E+155, but actual absolute error is 1.140714E+168.
gsl_sf_hyperg_0F1(i2d(0x1BDB9BF0824AECEA), i2d(0x22F7C93FACA8FCBB)) with estimate of the absolute error is 9.611187E+144, but actual absolute error is 2.234939E+157.
gsl_sf_clausen(i2d(0xC2D4C8E2EBF0F5E0)) with estimate of the absolute error is 1.808299E16, but actual absolute error is 1.153174E02.
gsl_sf_clausen(i2d(0x42AC3A936C2D0F3E)) with estimate of the absolute error is 2.047340E16, but actual absolute error is 7.243544E04.
gsl_sf_exprel_2(i2d(0xBF9C62E5D62AD9D9)) with estimate of the absolute error is 4.400140E16, but actual absolute error is 9.869315E04.
gsl_sf_psi_1(i2d(0xDFBE8E425E52DE59)) with estimate of the absolute error is 1.448389E13, but actual absolute error is 1.125952E+01.
gsl_sf_psi_1(i2d(0xC74262F4CCE814C6)) with estimate of the absolute error is 7.427255E14, but actual absolute error is 4.347871E+00.
gsl_sf_zeta(i2d(0xBFD85EC3692520C1)) with estimate of the absolute error is 3.307754E15, but actual absolute error is 1.283687E03.
gsl_sf_eta(i2d(0xBFD12087E34CCC81)) with estimate of the absolute error is 1.042941E14, but actual absolute error is 1.141164E03.
gsl_sf_gamma_inc_Q(i2d(0x3D6015265DC415D9), i2d(0x336A62C7B4081920)) with estimate of the absolute error is 8.881784E16, but actual absolute error is 6.319112E11.
gsl_sf_pochrel(i2d(0xD272424D4D731852), i2d(0x1EC8DCEFA40C71DF)) with estimate of the absolute error is 9.072393E14, but actual absolute error is 1.113754E+02.
gsl_sf_pochrel(i2d(0xCD88BA943FE1B3E9), i2d(0x3E47245280744497)) with estimate of the absolute error is 1.051328E13, but actual absolute error is 2.373726E+23.
gsl_sf_pochrel(i2d(0xCC1F1549401470B0), i2d(0x9547D22A7AE65BEC)) with estimate of the absolute error is 5.949131E14, but actual absolute error is 1.690742E+02.
gsl_sf_ellint_P(i2d(0x275AC794A3F9C13C), i2d(0x235BA8619CF10FD8), i2d(0x741226BBB54FE9F9)) with estimate of the absolute error is 1.842198E134, but actual absolute error is 4.148260E119.
We can see that in most cases the actual errors are many orders of magnitudes larger than the estimated ones, indicating potentially serious problems in practice.
Thanks,
Daming
