using sage libraries in python script: QQ and rational_field.py

[bjrnfrdnnd]

Hi,
I have installed sage 3.4 from source.
I want to use sage in my python scripts, particularly the linear
algebra part.
I therefore want to write little python scripts with something like

m=matrix([[1,2],[3,4]])
e=m.eigenvalues()

My only problem is: what should I import in order to make this kind of
thing work?

I figured out that you seemingly can import
import sage.all

This seems to reproduce the sage command-line functionality, i.e. I
can do

import sage.all
m=sage.all.matrix([[1,2],[3,4]])
e=m.eigenvalues()

However, I am not sure about that, and I did not find out where in
what manual this is explained.
And, I am importing a huge piece of software with this command.

Therefore, I want to try something else. Looking up "eigenvalues" in
the reference manual, I find that it resides in
sage.matrix.matrix2.Matrix

So, what I would like to do, is
import sage.matrix.matrix2
and then use Matrix.

However, this does not work: when trying to do this import,
python reports an error.

Here is the way to reproduce this error:

cd $SAGE_ROOT/loca/bin
source sage-env
./python
>>>import sage.matrix.matrix2
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "matrix2.pyx", line 1, in sage.matrix.matrix2 (sage/matrix/
matrix2.c:32616)
File "matrix1.pyx", line 1, in sage.matrix.matrix1 (sage/matrix/
matrix1.c:9974)
File "matrix0.pyx", line 32, in sage.matrix.matrix0 (sage/matrix/
matrix0.c:19609)
File "/home/bn/sage-3.4/local/lib/python2.5/site-packages/sage/
modules/free_module.py", line 163, in <module>
import free_module_element
File "free_module_element.pyx", line 111, in
sage.modules.free_module_element (sage/modules/free_module_element.c:
19756)
File "/home/bn/sage-3.4/local/lib/python2.5/site-packages/sage/rings/
arith.py", line 18, in <module>
import sage.rings.rational_field
File "/home/bn/sage-3.4/local/lib/python2.5/site-packages/sage/rings/
rational_field.py", line 52, in <module>
import rational
File "rational.pyx", line 63, in sage.rings.rational (sage/rings/
rational.c:17816)
File "real_mpfr.pyx", line 143, in sage.rings.real_mpfr (sage/rings/
real_mpfr.c:25879)
AttributeError: 'module' object has no attribute 'QQ'



What is going wrong? And how should I, in general, use sage in a
python script? Remember that there was no
way to find out from the eigenvalues entry in the reference manual
that you could actually import sage.all and use sage.all.matrix...
So I do actually not know how to figure out that kind of problems in
the future. If the
import sage.matrix.matrix2
would work,
I could use sage quite straightforwardly in my scripts, as I would
then be able to use the info in the reference manual.

Thank you for your help!

[William Stein]

On Sun, Mar 15, 2009 at 4:00 PM, bjrnfrdnnd <bjrnf...@googlemail.com> wrote:
>
> Hi,
> I have installed sage 3.4 from source.
> I want to use sage in my python scripts, particularly the linear
> algebra part.
> I therefore want to write little python scripts with something like
>
> m=matrix([[1,2],[3,4]])
> e=m.eigenvalues()
>
> My only problem is: what should I import in order to make this kind of
> thing work?
>
> I figured out that you seemingly can import
> import sage.all
>
> This seems to reproduce the sage command-line functionality, i.e. I
> can do
>
> import sage.all
> m=sage.all.matrix([[1,2],[3,4]])
> e=m.eigenvalues()
>
> However, I am not sure about that, and I did not find out where in
> what manual this is explained.
> And, I am importing a huge piece of software with this command.

To use any part of Sage you absolutely *MUST* import sage.all. Sage
is highly interdependent, and one can't just import little bits and
pieces.

> Therefore, I want to try something else. Looking up "eigenvalues" in
> the reference manual, I find that it resides in
> sage.matrix.matrix2.Matrix

This will segfault and fail horribly, so you shouldn't do it. Doing
"import sage.all" causes Sage to properly and in the right order
initialize itself - importing random things out doesn't.

-- William

--
William Stein
Associate Professor of Mathematics
University of Washington
http://wstein.org