From: SourceForge.net <noreply@so...>  20080908 14:08:23

Bugs item #635606, was opened at 20021108 12:47 Message generated for change (Comment added) made by dgildea You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=635606&group_id=4933 Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: Lisp Core  Limit Group: None >Status: Pending >Resolution: Fixed Priority: 5 Private: No Submitted By: Stavros Macrakis (macrakis) Assigned to: Nobody/Anonymous (nobody) Summary: limit(abs(log(x))) internal error, UND Initial Comment: Maxima 5.5/Windows/gcl limit(abs(log(x)),x,0) Error: The tag LIMIT is undefined. Should of course be INF. More controversially, perhaps, limit(log(x),x,0) gives UND  I believe it should give INFINITY; after all, limit(log (x),x,0,minus) gives INFINITY.  >Comment By: Dan Gildea (dgildea) Date: 20080908 10:08 Message: Logged In: YES user_id=1797506 Originator: NO As of limit.lisp rev 1.56: (%i6) limit(log(x), x, 0, minus); (%o6) minf+%i*%pi (%i7) limit(log(x), x, 0, plus); (%o7) minf (%i8) limit(abs(log(x)), x, 0, minus); (%o8) inf (%i9) limit(abs(log(x)), x, 0, plus); (%o9) inf (%i10) limit(abs(log(x)), x, 0); (%o10) inf (%i11) limit(1/x, x, 0, minus); (%o11) minf (%i12) limit(1/x, x, 0, plus); (%o12) inf (%i13) limit(1/x, x, 0); (%o13) infinity  Comment By: Stavros Macrakis (macrakis) Date: 20061109 18:45 Message: Logged In: YES user_id=588346 re limit(abs(log(x)),x,0) If we're working over real x and the complex log function, then if x>0, it should clearly be inf. If x<0, log(x) is not real, but abs(log(x)) is, and sure enough limit(abs(log(x)),x,0,minus) gives inf. This is I believe correct. And it's all consistent with limit(abs(log(x)),x,0) => inf. If on the other hand you take the position that limit operates on real functions, then negative x are not part of the domain of log(x), so we should look only at the limit for x>0, which also gives us the result inf. But limit is actually happy to return imaginary results, e.g. limit(sqrt(x),x,1) => %i. By the way, currently, limit(log(x),x,0,minus) gives minf+%i*%pi, which makes some sort of intuitive sense, but isn't really a valid expression  it should be infinity.  Comment By: Raymond Toy (rtoy) Date: 20061108 21:49 Message: Logged In: YES user_id=28849 The error no longer occurs in current CVS. It returns UND, after asking if x is positive or negative. Why should the answer be INF? log(x) is undefined for negative real x.  You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=635606&group_id=4933 