As the title says, sign(sqrt(-x^2-x^4)) => zero. This should give an "argument cannot be imaginary" error as does sign(sqrt(-1-x^2)).
A consequence of this bug is abs(sqrt(-x^2-x^4)) => 0.
Barton Willis
2013-02-27
Same bug, I suppose
$ ./maxima-local
Maxima 5.28.0_232_g5b9ec8e http://maxima.sourceforge.net
using Lisp Clozure Common Lisp Version 1.8-r15286M (WindowsX8664)
(%i1) assume(p <=0)$
(%i2) csign(sqrt(p));
(%o2) zero
Barton Willis
2013-02-27
The bug is almost surely in the function sign-mexpt--here is a portion of this
code. On the first line sign-base is $nz, so sign-base is set to $zero. After that
the global sign is set to sign-base. The final conditional doesn't have a clause for
$zero, so sign remains zero. A quick cure would be append a clause ((eq sign-base '$zero) ..., I suppose.
((eq sign-base '$nz) (setq sign-base '$zero) (tdzero base1)) (t (setq sign-base '$pz) (tdpz base1))))) (cond ((eq sign-expt '$neg) (cond ((eq sign-base '$zero) (dbzs-err x)) ((eq sign-base '$pz) (setq sign-base '$pos) (tdpos base1)) ((eq sign-base '$nz) (setq sign-base '$neg) (tdneg base1)) ((eq sign-base '$pnz) (setq sign-base '$pn) (tdpn base1))))) (setq sign sign-base)) ((eq sign-base '$pos) (setq sign '$pos)) ((eq sign-base '$neg) (if (eq evod '$odd) (setq sign '$neg) (setq sign (if *complexsign* '$complex '$pn)))))))
Robert Dodier
2013-05-24