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MathGroup Archive 2007

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Re: How to obtain numberical value from an

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80997] Re: How to obtain numberical value from an
  • From: rob <josh2499 at hotmail.com>
  • Date: Fri, 7 Sep 2007 02:09:07 -0400 (EDT)
  • References: <fbohh3$f5a$1@smc.vnet.net>

This looks interesting but what is it useful for? It appears 
one must already know the form of the inversefunction to 
apply it.  I feel sure I'm missing something; can someone 
point me to an actual practical use of this inversefunction 
concept? Thanks.


Bob Hanlon wrote:

> f[x_] := x;
> 
> f /: InverseFunction[f] = f;
> 
> InverseFunction[f][f[x]]
> 
> x
> 
> f[InverseFunction[f][x]]
> 
> x
> 
> InverseFunction[f][0.5]
> 
> 0.5
> 
> f[x_] := x^2;
> 
> f /: InverseFunction[f] = Sqrt;
> 
> InverseFunction[f][f[x]]
> 
> Sqrt[x^2]
> 
> f[InverseFunction[f][x]]
> 
> x
> 
> InverseFunction[f][4]
> 
> 2
> 
> 
> Bob Hanlon
> 
> ---- Nasser Abbasi <nma at 12000.org> wrote: 
> 
>>Hello;
>>
>>Are inverse function in Mathematica only have symbolic form and can't be 
>>used to evaluate numerically?
>>
>>Anything I am trying is not working, this is a very simple example:
>>
>>f[x_] := x
>>InverseFunction[f][x]
>>
>>Now, how to evaluate anything out of the above? say for x=0.5, I expected to 
>>get .5, but all I get is just
>>f(^-1)[x][.5]
>>
>>any ideas? Very little help on InverseFunctions.
>>
>>Nasser
>>
>>
> 
> 
> 


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