#90: (atanh -2)? --------------------+------------------------------------------------------- Reporter: rtoy | Owner: somebody Type: defect | Status: new Priority: major | Milestone: Component: Core | Version: 2013-12 Keywords: | --------------------+------------------------------------------------------- CMUCL 20e says {{{(atanh -2)}}} is {{{#C(-0.54930615 -1.5707964)}}}. This is consistent with what the CLHS says about {{{atanh}}} for {{{x < -1}}} being continuous with Quadrant III because {{{(atanh #c(-2.0 -0.0))}}} is the same. However, from the definition {{{ atanh(z) = 1/2*(log(1+z) - log(1-z)) }}} we have {{{ atanh(-2) = 1/2*(log(-1) - log(3)) = 1/2*(i*pi - log(3)) = -log(3)/2 + i*pi/2 }}} That is, the imaginary part should be positive. This would be consistent with the rule that atanh is continuous with Quadrant II. -- Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/90> cmucl <http://common-lisp.net/project/cmucl> Cmucl is a high-performance, free Common Lisp implementation.