Re: finding independent variable groups

*To*: mathgroup at smc.vnet.net*Subject*: [mg32431] Re: finding independent variable groups*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Sat, 19 Jan 2002 19:03:33 -0500 (EST)*References*: <a2b3mv$lhd$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

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. >