NSum working on Re[ ]
- To: mathgroup at smc.vnet.net
- Subject: [mg42953] NSum working on Re[ ]
- From: Mathijs Romans <m.w.j.romans at phys.uu.nl>
- Date: Wed, 6 Aug 2003 03:16:29 -0400 (EDT)
- Organization: Academic Computer Centre Utrecht, (ACCU)
- Sender: owner-wri-mathgroup at wolfram.com
I have problems applying NSum to a function that involves Re and Im, for
example:
ff[n_] := Re[Sqrt[n + I]];
NSum[ff[n], {n, 1, 100}]
Mathematica (4.2.0.0) gives an error because it does not know the
derivative of the Re-function. It wrongly assumes the chain-rule can be
applied: D[Re[f[x]],x] = Re'[f[x]]f'[x].
In this case of course I can circumvent the problem, but I have a though
calculation, and hope that is possible to set the derivative of a
general function Re[f[x]] correct, so an infinite numerical summation
becomes possible. Anybody knows any solutions? - Thanks