From: SourceForge.net <noreply@so...>  20111027 20:58:05

Bugs item #3429181, was opened at 20111027 08:40 Message generated for change (Comment added) made by crategus You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=3429181&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  Assume Group: None Status: Open Resolution: None Priority: 5 Private: No Submitted By: flyingfoxlee () Assigned to: Nobody/Anonymous (nobody) Summary: x^2<1 can't get x^2<2, but can get x^2<100 Initial Comment: Just like the summary, assume (x<1 and x>1), then is (x^<1) is true, but is (x^2<2) is undefined( so does 3 4 5 and 50 ,etc ), but is (x^2<100) is true again. What's happening here? Maxima version: 5.24.0 Maxima build date: 12:15 5/17/2011 Host type: x86_64unknownlinuxgnu Lisp implementation type: GNU Common Lisp (GCL) Lisp implementation version: GCL 2.6.7  >Comment By: Dieter Kaiser (crategus) Date: 20111027 22:58 Message: Again some examples to show the reported problem: (%i1) assume(abs(x)<1); (%o1) [abs(x) < 1] (%i2) sign(4x^2); (%o2) pos (%i3) sign(16x^2); (%o3) pos (%i4) sign(64x^2); (%o4) pos (%i5) sign(100x^2); (%o5) pos If the number has an integer root, Maxima can determine the sign. But not for a number, which has not an integer root. (%i6) sign(5x^2); (%o6) pnz The reason is within the algorithm of the Lisp function sign. Expressions are factored by the Lisp function signfactor to determine the sign. Maxima can evaluate the sign of the factored expression. (%i7) factor(4x^2); (%o7) (x2)*(x+2) (%i8) sign(%); (%o8) pos But for a number, which does not have an integer root, the expression can not be factored. For this case Maxima does not have an algorithm to evaluate the sign. (%i11) factor(5x^2); (%o11) (x^25) This might be called a missing feature. The Maxima function sign has a lot of more limitations. Dieter Kaiser  You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=104933&aid=3429181&group_id=4933 