Re: Simple question

*To*: mathgroup at smc.vnet.net*Subject*: [mg132202] Re: Simple question*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Thu, 16 Jan 2014 01:53:44 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net*References*: <20140115091656.DEBE169F0@smc.vnet.net>

Actually you do want to use ReplaceAll, you just don't want to manually enumerate all of the rules. expr = K11 Ue + (K12 - K21) Uex + K22 Uexx + (K23 + K32) Uexy + (K13 - K31) Uey + K33 Ueyy; expr2 = expr /. ((# -> D[U[x, y, z, t], Sequence @@ (ToExpression@ Characters@StringDrop[ToString@#, 2])]) & /@ Select[Variables[expr], StringMatchQ[ToString[#], "Ue*"] &]) Bob Hanlon On Wed, Jan 15, 2014 at 4:16 AM, KFUPM <hussain.alqahtani at gmail.com> wrote: > Dear All > > I have a long expression. Below is just a short part of it: > > K11 Ue + (K12 - K21) Uex + > K22 Uexx + (K23 + K32) Uexy + (K13 - K31) Uey + K33 Ueyy > > I want to replace Ue->U[x,y,z,t]. and Uex->D[U[x,y,z,t],x] and > Uexy->D[U[x,y,z,t],{x,y}] and so on. I want to make a command to scan the > expression and do the conversion autmatically. I don't want to use Replace > or ReplaceAll commands, because as I said, the command is very long and I > have so many functions to deal with. > > Many thanks in advance for your help. > > HMQ > >

**References**:**Simple question***From:*KFUPM <hussain.alqahtani@gmail.com>