trouble with solve()

[Stan Schymanski]

Dear all,

How can I get sage to solve a simple equation such as the one below?

----------------------------------------------------------------------
| Sage Version 4.0.2, Release Date: 2009-06-18 |
| Type notebook() for the GUI, and license() for information. |
----------------------------------------------------------------------
sage: var('x y n')
(x, y, n)
sage: solve(y == x^n,x)
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
[...]
TypeError: Computation failed since Maxima requested additional
constraints (try the command 'assume(>0)' before integral or limit
evaluation, for example):
Is n an integer?

MMA solves similar equation using inverse functions and spits out a
warning, no matter whether n is an integer or not. I thought that
Maxima would do the same as stated in the docu.

Here is an excerpt from the Maxima 5_15 docu:

"Let E be the expression and X be the variable. If E is linear in X
then it is trivially solved for X. Otherwise if E is of the form A*X^N
+ B then the result is (-B/A)^1/N) times the N'th roots of unity."

Is this a problem with the sage->maxima interface? I also wanted to
try Sympy as suggested in another post, but Sympy does not seem to be
included in the new version of sage any more. Am I misunderstanding
something?

Thanks for your help!

Stan

[Stan Schymanski]

Update:
In maxima, I simply have to answer 'no' to the question whether n is an
integer and I obtain the solution. How can I pass the 'no' to maxima
through sage??

Stan

--
________________________________________

Stan Schymanski
Scientist
Max Planck Institute for Biogeochemistry
Postfach 10 01 64
D-07701 Jena

Phone: +49.3641.576264
Fax: +49.3641.577274
WWW: http://www.bgc-jena.mpg.de/~sschym

Biospheric Theory and Modelling Group
http://www.bgc-jena.mpg.de/bgc-theory/
_________________________________________

[Kjetil Halvorsen]

On Fri, Jun 26, 2009 at 07:11, Stan Schymanski<schy...@gmail.com> wrote:
>
> Update:
> In maxima, I simply have to answer 'no' to the question whether n is an
> integer and I obtain the solution. How can I pass the 'no' to maxima
> through sage??
>

Try to use assume() befotre the call to maxima?

--
"... an entire human genome would fit on a music CD."

--- www.thinkgene.com

[Stan Schymanski]

Thanks, but this does not help in this case:

----------------------------------------------------------------------
| Sage Version 4.0.2, Release Date: 2009-06-18 |
| Type notebook() for the GUI, and license() for information. |
----------------------------------------------------------------------
sage: var('x y n')
(x, y, n)

sage: assume(n,'real')

sage: solve(y == x^n,x)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
...
TypeError: Computation failed since Maxima requested additional
constraints (try the command 'assume(>0)' before integral or limit
evaluation, for example):
Is n an integer?

This even happens in maxima. No matter what I assume for n, it is still
possible that it is an integer, so maxima keeps asking. Only if I assume
that it is indeed an integer, it will evaluate, but this assumption is
wrong as n does not need to be an integer. So the assume() method allows
passing the answer 'yes', but not the answer 'no' in this case.

Stan