Re: Extracting free parameters from a Solve result

• To: mathgroup at smc.vnet.net
• Subject: [mg93945] Re: [mg93914] Extracting free parameters from a Solve result
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Sat, 29 Nov 2008 04:31:21 -0500 (EST)

```rules = {{W11 -> W44, W12 -> -W34, W13 -> W34,
W14 -> -W23 - W33 + W44, W22 -> W33, W24 -> -W34}};

pars = Variables[Last /@ rules[[1]]]

{W23,W33,W34,W44}

Bob Hanlon

=============
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.

--

Bob Hanlon

```

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