R (Chandra) Chandrasekhar wrote:
> Dear Folks,
>
> Pardon for the double-posting since I am unsure which list is more
> appropriate.
>
> In section 2.4.1 of the Sage Tutorial, there is a non-linear equation
> example from Jason Grout that I tried out, but it failed. Details follow.
>
> My version is built from the Ubuntu jaunty package source and runs on a
> Kubuntu Intrepid AMD 64 PC. The startup banner is
>
> ----------------------------------------------------------------------
>
> | SAGE Version 3.0.5, Release Date: 2008-07-11 |
>
> | Type notebook() for the GUI, and license() for information. |
>
> ----------------------------------------------------------------------
>
> When I load the file with these contents for the example:
> ===
> var('x y p q')
> (x, y, p, q)
> eq1 = p+q==9
> eq2 = q*y+p*x==-6
> eq3 = q*y^2+p*x^2==24
> solve([eq1,eq2,eq3,p==1],p,q,x,y)
> ===
>
> I get this error (with directory paths anonymized):
> ---------------------------------------------------------------------------
>
> ValueError Traceback (most recent call
> last)
>
> /Path-To-File_non_linear_eq_sage_0.py in <module>()
>
> 8 eq2 = q*y+p*x==-Integer(6)
>
> 9 eq3 = q*y**Integer(2)+p*x**Integer(2)==Integer(24)
>
> ---> 10 solve([eq1,eq2,eq3,p==Integer(1)],p,q,x,y) 11
> 12
>
> /usr/lib/python2.5/site-packages/sage/calculus/equations.pyc in solve(f,
> *args, **kwds)
> 1386 s = m.solve(args)
> 1387 except:
> -> 1388 raise ValueError, "Unable to solve %s for %s"%(f, args)
> 1389 a = repr(s)
> 1390 sol_list = string_to_list_of_solutions(a)
>
> ValueError: Unable to solve [q + p == 9, q*y + p*x == -6, q*y^2 + p*x^2
> == 24, p == 1] for (p, q, x, y)
> WARNING: Failure executing file: <Path-To-File_non_linear_eq_sage_0.py>
> ---------------------------------------------------------------------------
>
> The version of the tutorial that I am using came with the version of
> Sage installed. So, I do not think it is a version incmpatibility problem.
>
> Can someone tell me what the workaround is, or whether I need to file a
> bug report.
I'm not sure what is going on here. Version 3.0.5 is from quite a while
ago, at least in Sage terms. The calculation works great in the current
version of Sage (version 3.4, just released yesterday, as tested on
http://www.sagenb.org.) Did you say that this was from the jaunty
source, as in the debian packaging of Sage? Does running "sage -maxima"
run maxima? Can you solve simpler equations?
That said, when I read the tutorial, I thought it was kind of awkward to
have my name be the only name on that page; surely other people
contributed the many, many examples on that page. If there should be a
reference, then maybe a reference to the paper the calculation came from
would be in order (http://arxiv.org/abs/0710.5669), but I wouldn't think
that would even be necessary unless you were also trying to make the
point that Sage is used in published research, even with simple algebra.
Thanks,
Jason
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