Hi guys
apologies as usual for how dumb this question's going to sound ... but how
do I actually *use *the variables a[1] etc? What I was hoping to do was to
use them in the following way (once I had already apparently successfully
invoked Jason's routine), where d is a variable I would like to be able to
change:
d = 5;
for ii in range(0,d):
for a[ii] in range(0,d):
print a[ii]^2 + ii;
but I get "TypeError: 'VariableGenerator' object does not support item
assignment" seemingly no matter what variant I try.
Thanks for any pointers!
kind regards
Gary
On Tuesday, July 5, 2011 1:05:32 AM UTC+1, Jason Grout wrote:
>
> This question has come up often enough that I thought posting a short
> snippet here might be useful. The question is: how do I automatically
> generate variables based on indices (e.g., a[0], a[1], etc. being
> variables). Here is one way:
>
> class VariableGenerator(object):
> def __init__(self, prefix):
> self.__prefix = prefix
>
> @cached_method
> def __getitem__(self, key):
> return SR.var("%s%s"%(self.__prefix,key))
>
> Now just specify a prefix, and then you can index to your heart's
> content to generate variables.
>
> a=VariableGenerator('a') # some people may like 'a_' as the prefix
> a[0], a[1], a[2] # all variables
>
> Of course, this can easily be extended to using function call syntax:
> a(0), or to using multiple indices: a[1,3]. Indeed, you can let your
> imagination run wild and even do things like return full symbolic
> matrices or vectors with slices: a[0:5, 0:5].
>
> Perhaps this is useful enough to be in Sage instead of just a snippet
> here too...
>
> Thanks,
>
> Jason
>
> --
> Jason Grout
>
>
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