Re: How to substitute?

*To*: mathgroup at smc.vnet.net*Subject*: [mg45499] Re: How to substitute?*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Sat, 10 Jan 2004 00:00:49 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 1/9/04 at 5:20 AM, stevebg at adelphia.net (Steve Gray) wrote: > \!\(\((y\_0 - z\_3)\)\ \((\(-y\_1\) + z\_3)\)\ \((\(-y\_2\) + > z\_3)\)\ \((\(-y\_3\) + z\_3)\)\) > I have output cells containing various expressions such as > (y[0]-z[1]) (y[1]-z[2]) (y[4] - z[0]), where I use [x] here to mean > subscript. The integers can have any small values. For compactness of > expression, I want to make substitutions which make the above > expression look like Q[0,1]Q[1,2]Q[4,0]. There are many combinations > of subscript pairs and I don't want to write explicit substitution > rules for every possible combination. I tried doing /.(y[i]-z[j]) -> > Q[i,j] , and /.(y[i_]-z[j_]) -> Q[i,j] but they don't work. These substitutions work fine when done properly. Try (Subscript[y, 0] - Subscript[z, 3])*(-Subscript[y, 1] + Subscript[z, 3])*(-Subscript[y, 2] + Subscript[z, 3])* (-Subscript[y, 3] + Subscript[z, 3]) /. Subscript[y, i_] - Subscript[z, j_] -> Subscript[Q, i, j] (Subscript[z, 3] - Subscript[y, 1])* (Subscript[z, 3] - Subscript[y, 2])* (Subscript[z, 3] - Subscript[y, 3])*Subscript[Q, 0, 3] -- To reply via email subtract one hundred and four