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MathGroup Archive 2005

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Re: Re: sqrt(x^2) = x

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61224] Re: [mg61189] Re: sqrt(x^2) = x
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Thu, 13 Oct 2005 01:39:33 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

Changing the definition of a built-in function is dangerous since it may have 
unintended side effects. I recommend that you use something like

Clear[mySqrt];
mySqrt[a_.*x_^2]:=mySqrt[a]*x;
mySqrt[a_?AtomQ]:=Sqrt[a];

convertSqrt=Power[x_,Rational[1,2]]:>mySqrt[x];

{Sqrt[x^2],Sqrt[a*x^2],Sqrt[Pi*x^2*y^2]}/.convertSqrt

{x, Sqrt[a]*x, Sqrt[Pi]*x*y}


Bob Hanlon

> 
> From: "Francisco Javier" <pacoga at ctv.es>
To: mathgroup at smc.vnet.net
> Date: 2005/10/12 Wed AM 01:42:23 EDT
> Subject: [mg61224] [mg61189] Re: sqrt(x^2) = x
> 
> Francisco Javier a formulé ce martes :
> > Dear all, I am new in this group
> >
> > How can I tell Mathematica that I want to simplify all expressions like 
> > Sqrt[x^2] as x, whithout taking into account that x is or not a 
> > positive real number?
> >
> > Thank you very much
> 
> Dear F.Jaccard and Ruth for your answers, but what I really mean has 
> not a such simple solution.
> 
> I want to "teach" to Mathematica that in next calculations Sqrt[x^2] is 
> equivalent to x,
> 
> I have tried
> 
> Unprotect[Sqrt];
> Sqrt[(x_)^2] := x;
> 
> This seems works fine then with calculations like
> 
> Sqrt[y^2]
> y
> 
> but it fails with
> 
> Sqrt[x^2 y^4]
> 
> or even with
> 
> Sqrt[x^2 y^4]
> 
> Any ideas?
> 
> -- 
> ----
> Francisco Javier García Capitán
> http://garciacapitan.auna.com
> 
> 



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