feature request: erfc() and expm1()

[MathGeniusJodie]

would it be possible to add functions like erfc and expm1 for extra precision around zero?

[samhocevar]

I can easily add expm1, yes. However I have been unable to find a good way to compute erfc so far, the formulae I found were either incredibly slow or inaccurate.

[MathGeniusJodie]

awesome, shame about erfc, I'm making a math library and I've been finding it hard to approximate it

[samhocevar]

Hi! I have added expm1 and log1p to the main branch.

I’ll have another look at erfc.

[samhocevar]

Hi! I have added the erfc() and erfcx() functions. So I’ll be closing this issue.

Maybe the accuracy issues in erfc() will not be a big deal to you; the maximum error is 1.6e-44 (see this issue).