Re: Extracting free parameters from a Solve result
- To: mathgroup at smc.vnet.net
- Subject: [mg93932] Re: Extracting free parameters from a Solve result
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Fri, 28 Nov 2008 07:12:13 -0500 (EST)
- Organization: Uni Leipzig
- References: <ggog1b$s65$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
Hi,
expr = {{W11 -> W44, W12 -> -W34, W13 -> W34, W14 -> -W23 - W33 + W44,
W22 -> W33, W24 -> -W34}};
Union[Cases[expr /. (_ -> a_) :> a, _Symbol, Infinity]]
??
Regards
Jens
carlos at colorado.edu wrote:
> In solving a Sylvester matrix equation, Solve is given
> 18 equations in 10 variables: v= {W11,W12,W13,W14,W22,
> W23,W24,W33,W34,W44} It returns
>
> {{W11->W44, W12->-W34, W13->W34,
> W14->-W23-W33+W44, W22->W33, W24->-W34}}
>
> How do I extract the 4 variables: W44,W34,W23,W33 left
> over on the right of the ->, and place them in an ordered list:
>
> pars={W23,W33,W34,W44}
>
> I guess the simplest way would be to Drop the dependent
> variables from the v list but the details escape me. Thanks.
>