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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