Q function (inverse) and erf(c) inverse in CAS

[nbc12]

(07-22-2024 05:50 PM)Albert Chan Wrote:  

(07-22-2024 04:52 PM)nbc12 Wrote:  erfcinv(x):=normald_icdf((x/2)/-√(2));

Typo. Should be:

erfcinv(x) := normald_icdf(x/2) / -√(2);

Quote:qfunc(x):=(1/2)*erfc(x/√(2))
qfuncinv(x):=(√(2))*erfcinv(2*x)

Nothing wrong with these, but perhaps simpler with cdf / icdf

qfunc(x) := normald_cdf(-x);
qfuncinv(x) := -normald_icdf(x);

Good catch, I changed the original post to match. And yes, you are right, it is much simpler using cdf and icdf!