Re: Summation convention
- To: mathgroup at christensen.cybernetics.net
- Subject: [mg222] Re: [mg204] Summation convention
- From: Richard Mercer <richard at rmercer.wright.edu>
- Date: Wed, 23 Nov 1994 12:34:10 -0500
> Dear Mathgroupers,
>
> I wonder if you could help me,
>
> I need to set up a rule of the following form,
>
> rule = {b[a[x_]] -> d[a[y],a[x]] c[a[y]]},
>
> where a[y] must differ from all other indices a[k] used
> so far. My application involves expressions involving
> use of the summation convention which I would like to
> manipulate using Mma. Thus, in "rule" given above, the
> RHS is interpreted as being summed over the index a[y].
> I need to ensure that, in any given complicated
> expression, that if
>
> e = b[a[1]] b[a[2]]
>
> and each b[a[j]] (j=1,2) is to be replaced by a term
> involving summation using the above "rule", that the
> indices using in each summation are different. One thing
> I thought of involved incrementing the summation index
> y in "rule" each time I used it, but this would not work
> as if I write
>
> f = e /. rule
>
> "rule" is applied twice before I have a chance to
> increment y.
>
> Any suggestions? (I am actually away for the next week,
> but I look forward to reading email on my return!),
>
> Thanks, Stephen
>
If I understand your question correctly, you will find the Unique
command useful, e.g.
Unique["y"]
will generate a variable of the form yn where n is an integer,
and yn has not been used IN THIS SESSION.
*********************************************************************
Richard Mercer 513-873-2191 office
Department of Mathematics and Statistics 513-873-2785 message
Wright State University 513-429-2179 fax
Dayton, OH 45435 NeXTmail welcome!
richard at rmercer.wright.edu or rmercer at desire.wright.edu
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