Working with indefinite number of variables
- To: mathgroup at smc.vnet.net
- Subject: [mg129095] Working with indefinite number of variables
- From: Benjamin Hell <hellben at gmx.de>
- Date: Sat, 15 Dec 2012 05:47:49 -0500 (EST)
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Hi,
I have been wrapping my head around this for a while now and I have not found a solution so far.
I want to work with an indefinite number of variables in mathematica and use some built in functions.
To make things more specific for starters I want to do the following:
Define a sum with n summands each containing a new variable x[i] (in the i-th summand):
sum[n_] = Sum[i*x[i], {i, 1, n}]
Then I want to differentiate the expression with respect to some x[i] like:
D[sum[n],x[2]]
Mathematica return 0 instead of 2. If I supply a specific n like:
D[sum[2],x[2]]
everything works fine.
I thought about using Assumptions for n, but with no success so far.
How can I do that right?