Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
Drexel University or The Math Forum.
|
|
|
|
Re: [mg4433] Replacement
Posted:
Jul 30, 1996 2:58 AM
|
|
ges@vsnhdd.cern.ch (Sergej Gerassimov)
[mg4433] Replacement
writes
> I have something like
> x/Sqrt[a^2+b^2]+Sqrt[a^2+b^2]/y
> and I'd like to substitute Sqrt[a^2+b^2] by r.
>
> x/Sqrt[a^2+b^2]+Sqrt[a^2+b^2]/y //. Sqrt[a^2+b^2]->r
> gives:
>
> x r
> ------------- + -
> Sqrt[a^2+b^2] y
>
> (replace one only in the numerator)
> How to replace Sqrt[a^2+b^2] by r everywhere in the expression?
Serge:
Two suggestions
x/Sqrt[a^2+b^2]+Sqrt[a^2+b^2]/y /.
{Power[(a^2+b^2), p:1/2|-1/2]->r^Sign[p]}
x r
- + -
r y
x/Sqrt[a^2+b^2]+Sqrt[a^2+b^2]/y /.
{Sqrt[a^2+b^2]->r,1/Sqrt[a^2+b^2] ->1/r}
x r
- + -
r y
The reason is that what Mma sees is
FullForm[x/Sqrt[a^2+b^2]+Sqrt[a^2+b^2]/y]
Plus[
Times[Power[Plus[Power[a, 2], Power[b, 2]], Rational[-1, 2]], x],
Times[
Power[Plus[Power[a, 2], Power[b, 2]], Rational[1, 2]],
Power[y, -1]
]
]
The Sqrt has gone.
Allan Hayes
hay@haystack.demon.co.uk
|
|
|
|
