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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)
  • Reply-to: hanlonr at cox.net

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

---- 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.


--

Bob Hanlon



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