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Re: finding independent variable groups


Ioan,
Assuming that you do not want the expression to evaluate before determining
or acting at the positions, here are two suggestions (I have added an extra
x/y)

    Rest/@Position[Hold[(x/y) Exp[z x/y]],x/y]

    {{1},{2,1,2}}

    Hold[(x/y) Exp[z x/y]]/.x/y->u

          Hold[u*E^(z*u)]#

Now remove Hold

    ReleaseHold[%]

        E^(u*z)*u


--
Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565


"Ioan Alexandre Romoscanu" <romoscanu at imes.mavt.ethz.ch> wrote in message
news:a2b3mv$lhd$1 at smc.vnet.net...
> I wonder if it is possible to do the following formula manipulation
> task with Mathematica.
>
> Suppose you have a function of 3 variables [x,y,z], where only the
> ratio x/y occurs. Example
>
> f[x_,y_,z_]=(x/y) Exp[z]
>
> If now you have a large formula of more than 3 variables, where
> however certain variables always occur grouped together, in the same
> pattern (like x and y above).
>
> Is there a way to make Mathematica find out such groups of variables
> in a larger expression?
>
> Thank you for any help
>
> A.I.R.
>




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