Re: I do not understand
- To: mathgroup at smc.vnet.net
- Subject: [mg25440] Re: I do not understand
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Sun, 1 Oct 2000 02:44:23 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <8r180o$hin@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
y'[t] is internal written as
Derivative[1][y][t] and this can't match a rule for y[t].
If you plan to replace derivatives you should use a construction like
y'[t] /. Thread[{#, D[#, t]} & /@ (y[t] -> ySer)]
In the fitst case
y[t] + y'[t] /. y[t]->ySer
only y[t] is replaced but Mathematica see a sum with
a series and expand y'[t] also to an series.
Regards
Jens
Borut L wrote:
>
> Hello,
>
> ySer=Series[y[t],{t,0,3}]
>
> If I apply this rule like this
> (y[t]+y'[t])/.y[t]->ySer
> both y[t] and y'[t] changes appropriately
>
> If I apply
> y'[t]/.y[t]->ySer
> nothing happens
>
> Why is that?