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MathGroup Archive 2004

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Re: changing replacement rule arrow ( ->) to equal sign(==)...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45890] Re: changing replacement rule arrow ( ->) to equal sign(==)...
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 29 Jan 2004 05:34:36 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <bv83l0$idm$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

{G[0] -> 4*(5 - 2*Sqrt[6]), tfC[0] -> 2*(5 - 2*Sqrt[6]),
 C[0] -> 3 - Sqrt[6], tf[0] -> 3 - Sqrt[6]} /. Rule->Equal

may help you.

Regards
  Jens

sean kim wrote:
> 
> thanks for all those tho replied regarding adding interpoating
> functions.
> 
> few more questions...
> 
> let's say you can Solve a system of equations like this.
> 
> In[267]:=
> itxn = Solve[{0 == 1 - 2C[t] - 1 C[t] tf[t] + 2 tfC[t],
>           0 == -1  G[t] + 2 tfC[t],
>           0 == 1 - 2 tf[t] - 1 C[t] tf[t] + 2 tfC[t],
>           0 == 1 C[t] 2 tf[t] - 1 tfC[t] - 2 tfC[t]}, {C[t], G[t],
> tf[t],
>           tfC[t]}][[1]] /. t -> 0
> 
> above give a replacement rule as below.
> 
> {G[0] -> 4*(5 - 2*Sqrt[6]), tfC[0] -> 2*(5 - 2*Sqrt[6]),
>  C[0] -> 3 - Sqrt[6], tf[0] -> 3 - Sqrt[6]}
> 
> now I would like to use this rule asd part of NDSolve as initial
> conditions. but as we all know, it can't be used directly.
> 
> the -> needs to be replaced with ==
> 
> now, if i try to Map a rule that replaces -> with ==, like...
> 
> Map[{itxn[[1]] == itxn[[2]]}, itxn]
> 
> it doesn't work.
> 
> it gives a long list with wrong result.
> 
> what i wanted though is
> {G[0] == 4*(5 - 2*Sqrt[6]), tfC[0] == 2*(5 - 2*Sqrt[6]),
>  C[0] == 3 - Sqrt[6], tf[0] == 3 - Sqrt[6]}
> 
> So, what i would like to do is use the results from the Solve directly
> in NDSolve as the initial conditions without having to manually edit
> out the arrows with equal signs.
> 
> can you guys please shed some light on this matter?
> 
> thank you very much in advance
> 
> sean


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