       Re: Symbolic summation

• To: mathgroup at smc.vnet.net
• Subject: [mg101608] Re: [mg101561] Symbolic summation
• From: Jaebum Jung <jaebum at wolfram.com>
• Date: Fri, 10 Jul 2009 23:24:44 -0400 (EDT)
• References: <200907101044.GAA15502@smc.vnet.net>

```Luca wrote:
> Hello all, I have a problem, I've to compute a symbolic summation, which takes a very long time if I have to do it by hand. I have to write the terms of the Volterra series, related to the associated linear equation of a system.
>
> The problem is that I'm not really confident with mathematica, I've tried to use symbolic calculations with sums, but I think that in my case is not so easy.
>
> The problem is that I want a solution of this form:
>
> x1+x2+x3+x4+x5...
>
> Where the 1, 2, 3 and 4 and 5 are the summation subscripts...
>
> My summation is not infinite, I have to stop it.
>
> If I write something like this:
>
> n = 3;
>
> Sum[kl, {l, 2, n}]
>
> I obtain 2kl, instead I want to obtain k2+k3.
>
> Is it possible with mathematica?
>
>

kl regarded as one symbol.   one way is using k[l] instead of kl and
then convert it to kl.   For example,

tosymbol[s_[t_]] := ToExpression[ToString[Row[{s, t}]]]

In:= Sum[k[l],{l,2,n}]
Out= k+k
In:= tosymbol/@%
Out= k2+k3

In:= Sum[tosymbol@k[l],{l,2,n}]

Out= k2+k3

In:= Sum[k[l],{l,2,n}]/.k[x_]:>tosymbol[k[x]]
Out= k2+k3

- Jay

```

• Prev by Date: Re: Symbolic summation
• Next by Date: Re: Re: Calculate n in binomial distribution
• Previous by thread: Re: Symbolic summation
• Next by thread: Re: Symbolic summation