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bool gives another unexpected result

asked 2011-06-20 22:23:48 +0200

omoplata gravatar image

updated 2013-06-03 11:16:48 +0200

tmonteil gravatar image

Here is the output

sage: var('c,u,v',domain=RR);assume(v>0,u>0,c>u,c>v);
(c, u, v)
sage: assumptions()
[v > 0, u > 0, c > u, c > v]
sage: bool(c^2 - u*v >= 0)
sage: bool(c^2 - u^2 >= 0)
sage: bool(c^2 - v^2 >= 0)

I don't see how c^2 - v*u can not be larger than or equal to zero. Why does this happen? Is there a workaround?

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answered 2011-06-21 09:18:55 +0200

niles gravatar image
sage: bool(c^2 - u*v >= 0)

"False" here means "not known to be true" -- it seems that bool just can't make the following observation:

c^2 > c*v > u*v

Although if you test each inequality separately, it will recognize them as True. More powerful symbolic manipulation is available through Maxima; see for example the parts of the reference manual having to do with Symbolic Calculus.

Unfortunately you might have to work harder for this -- I tried test_relation_maxima and got the same unsatisfactory results as with bool. You could try looking through the Maxima reference manual to see if there is something more useful there. You can use Maxima directly through Sage with maxima_console():

sage: maxima_console()
;;; Loading #P"/Applications/sage/local/lib/ecl/sb-bsd-sockets.fas"
;;; Loading #P"/Applications/sage/local/lib/ecl/sockets.fas"
;;; Loading #P"/Applications/sage/local/lib/ecl/defsystem.fas"
;;; Loading #P"/Applications/sage/local/lib/ecl/cmp.fas"
Maxima 5.23.2
using Lisp ECL 11.1.1
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) factor(10!);
                                   8  4  2
(%o1)                             2  3  5  7
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The symbolic ring will automatically fall back to maxima if pynac alone can't figure out if a relation is true.

Volker Braun gravatar imageVolker Braun ( 2011-06-21 14:27:20 +0200 )edit

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Asked: 2011-06-20 22:23:48 +0200

Seen: 265 times

Last updated: Jun 21 '11