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Re: format of "Solve" output

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59934] Re: [mg59923] format of "Solve" output
  • From: "benshimo at bgumail.bgu.ac.il" <bsyehuda at gmail.com>
  • Date: Fri, 26 Aug 2005 04:53:24 -0400 (EDT)
  • References: <200508190831.EAA27442@smc.vnet.net> <200508251034.GAA10188@smc.vnet.net>
  • Reply-to: benshimo at bgumail.bgu.ac.il
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,
replacing your Out[25] with sol
that is
sol={{x -> a + b, y -> 2 a + b}};
Then there is no way that
Fold[And, 1, Apply[Equal,sol[[1]], {1}]]
will generate strings as you described.
Actualy it generates,
1 && x == a + b && y == 2 a + b
and FindInstance cannot process this
yehuda

On 8/25/05, Ed Peschko <esp5 at mdssdev05.comp.pge.com> wrote:
>
> hey all,
>
> I had a simple question that I can't find a simple answer for in the docs :
>
> When you solve an equation using 'Solve', it comes out in the format:
>
> {{ x -> a+b, y -> 2 a + b}}
>
> However, when you try to transform the equations for use in FindInstance,
> say by using:
>
>
> Fold[And, 1, Apply[Equal, %25[[1]], {1}]]
>
> you get:
>
> "x" == "a" + "b" && "y" + 2 "a" + "b"
>
> In other words, variables lose their variableness. So, when you
> plug the results into, say, FindInstance it complains that "a" is not
> a variable.
>
> Is there any reason for this? And how can you turn the character strings
> back into variables?
>
> Thanks,
>
> Ed
>
>



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