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MathGroup Archive 2005

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Re: odd mathematica blindspot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56472] Re: [mg56468] odd mathematica blindspot
  • From: yehuda ben-shimol <bsyehuda at gmail.com>
  • Date: Tue, 26 Apr 2005 21:52:28 -0400 (EDT)
  • References: <200504260533.BAA14442@smc.vnet.net>
  • Reply-to: yehuda ben-shimol <bsyehuda at gmail.com>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,
First Mathematica solves it with no problem. I wonder which version
you are using. I tested it on ver. 5.1 on Win XP.
Second, the (rather simple) problem is
Solve[a^x==b,x] will return
{{x->Log[b]/Log[a]}}
so if you assign 
sol = Solve[a^x==b,x];
you can check it for many values of a and b which in your case will lead to
sol={{x->-Log[2]/Log[(999999999999/10000000000000)]}}
to extract this value you need to use replacement rules
x/. sol[[1]] will give you the number
x/.sol will give you the number as a list of a single element.
yehuda

On 4/26/05, Edward Peschko <esp5 at pge.com> wrote:
> hey all,
> 
> I was wondering why the following didn't output any solutions. I'd think
> it would be easy:
> 
>         Solve[(999999999999/10000000000000)^x == .5, x]
> 
> It gives no solutions. What's really odd is when you say:
> 
>         Solve[(999/1000)^x==.5, x]
> 
> which *does* give solutions, in the form:
> 
>         {{x -> 692.801... }}
> 
> Also, just curious, but how do you extract 'x' from the above?
> Say I wanted to plug the above solution into another equation..
> In perl I'd say something like:
> 
> y = Solve[(999/1000)^x == .5, x];
> 
> 3 * y->{x}  # replaces with 692.81
> 
> etc. etc.
> 
> but this doesn't seem to work. How do you access parts of a mathematica
> datastructure/hash?
> 
> And finally, how do you set values with the tty? ie: suppose my backspace and
> delete key aren't working with math.exe (they aren't) and I want them to
> delete typos. In unix this would be stty erase ^H. In mathematica...?
> 
> Thanks much for any help,
> 
> Ed
> 
>


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