Ask Your Question

bool gives another unexpected result

asked 2011-06-20 15:23:48 -0500

omoplata gravatar image

updated 2013-06-03 04:16:48 -0500

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?

edit retag flag offensive close merge delete

1 answer

Sort by ยป oldest newest most voted

answered 2011-06-21 02:18:55 -0500

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
edit flag offensive delete link more


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 07:27:20 -0500 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

[hide preview]

Question Tools


Asked: 2011-06-20 15:23:48 -0500

Seen: 62 times

Last updated: Jun 21 '11