On Feb 1, 2008 7:40 AM, Peter Storm <[EMAIL PROTECTED]> wrote:
> Professor Stein,
>
> In the course of my research ambling, I believe I may have come across
> a small bug in sage. In a few emails I discussed it with Justin
> Walker, and he thought it merits submission.
>
> In case you're interested, I have included the bug report I intend to
> submit below.
>
> Thank you,
> Pete Storm
> --
> Mathematics Department
> University of Pennsylvania
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%
>
> BUG REPORT
>
> I have sage-2.10 installed on my macpro running Debian lenny. (Sorry
> Justin.) It was installed from source code. I did not alter the
> code. The command
>
> ./sage -testall
>
> returned 0 failed tests.
>
> Here is an excerpt from my recent session:
>
> {{{
>
> sage: version()
> 'SAGE Version 2.10, Release Date: 2008-01-18'
> sage: M = FreeModule(Integers(), 2)
> sage: 2*M
> ---------------------------------------------------------------------------
> <type 'exceptions.TypeError'> Traceback (most recent call last)
>
> /home/storm/.sage/<ipython console> in <module>()
>
> /home/storm/.sage/element.pyx in sage.structure.element.RingElement.__mul__()
>
> /home/storm/.sage/coerce.pyx in
> sage.structure.coerce.CoercionModel_cache_maps.bin_op_c()
>
> <type 'exceptions.TypeError'>: unsupported operand parent(s) for '*':
> 'Integer Ring' and '<class
> 'sage.modules.free_module.FreeModule_ambient_pid'>'
> sage:
>
> }}}
>
> On the webpage
>
> http://www.msri.org/about/computing/docs/sage/ref/module-sage.modules.free-module.html#l2h-3124
>
> of the documentation one can find the following identical example:
>
> {{{
>
> sage: M = FreeModule(Integers(), 2)
> sage: 2*M
> Free module of degree 2 and rank 2 over Integer Ring
> Echelon basis matrix:
> [2 0]
> [0 2]
>
> }}}
>
The problem is that the documentation you referee to is about 2 years old, and
Sage is 3 years old, and that functionality has been deprecated. In the
current version of Sage the correct thing to do is use the scale method:
sage: M = FreeModule(Integers(), 2)
sage: M.scale(2)
Free module of degree 2 and rank 2 over Integer Ring
Echelon basis matrix:
[2 0]
[0 2]
sage: M.scale(1/2)
Free module of degree 2 and rank 2 over Integer Ring
Echelon basis matrix:
[1/2 0]
[ 0 1/2]
> Clearly, my computer did not produce the intended output. My
> theory is that, for some reason, sage never checks to see if __rmul__
> is a method for the object M. (This is what python would do.)
> Perhaps recent work on coercion has caused this crucial step to be
> skipped.
>
> I have observed similar problems with test classes I've created. In
> general, it appears that sage does not look for an __rmul__ method
> before returning an error.
>
> Thank you for any help you can give.
>
> Best,
> Pete Storm
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
--
William Stein
Associate Professor of Mathematics
University of Washington
http://wstein.org
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