Hi guys,
Thanks for the insights. I knew that trying to define the generators
in my original way was asking for trouble, but it's good to learn
why. Right now, I just did the simple thing (which I should have done
from the start):
class DifferentialForms(Algebra):
def __init__(..., coordinates = ('x', 'y', 'z')):
# Create a dz for every z in coordinates
This way I can avoid any confusion with the 'names' keyword.
The "preparse" command is pretty cool!
All the best,
Joris
On 18 mei, 18:30, Jason Grout <jason-s...@creativetrax.com> wrote:
> On 05/18/2010 11:14 AM, John Cremona wrote:
>
> > In our example, how does DifferentialForms() know that there are three
> > variables?
>
> > Also, note that the syntax F.<x,y,z> = ... would normally be a
> > shorthand for something like F = ....; x,y,z = F.gens().
>
> Good point. Joris, the <x,y,z> syntax is just syntactic sugar that is
> preparsed into:
>
> sage: preparse('F.<x,y,z>=DifferentialForms()')
> "F = DifferentialForms(names=('x', 'y', 'z',)); (x, y, z,) =
> F._first_ngens(3)"
>
> So you can see from the "(x,y,z,)=..." statement that you are in reality
> defining the variables "x", "y", and "z", and there is nothing a class
> can do about that without changing the preparser.
>
> In fact, if I wanted to call what you call "dx" by the name "x", I
> suppose that is my business, regardless of how many conventions it
> messes up :).
>
> In that sense, would it be so hard to expect the user to do something like:
>
> F.<dx,dy,dz>=DifferentialForms()
>
> which preparses into
>
> sage: preparse('F.<dx,dy,dz>=DifferentialForms()')
> "F = DifferentialForms(names=('dx', 'dy', 'dz',)); (dx, dy, dz,) =
> F._first_ngens(3)"
>
> Thanks,
>
> Jason
>
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