Re: Delayed Derivative Operator

*To*: mathgroup at smc.vnet.net*Subject*: [mg81792] Re: Delayed Derivative Operator*From*: Peter Breitfeld <phbrf at t-online.de>*Date*: Wed, 3 Oct 2007 06:12:32 -0400 (EDT)*References*: <fdvd73$so5$1@smc.vnet.net>

ToddSmith schrieb: > Hi, > I would like to be able to have an equation > > eq := D[f[x],x]==5; > > And a substitution rule > > rule = f[x]->x^3; > > And perform the substitution > > eq/.rule > > And get back the equation 3x^2==5. But Mathematica sees f'[x] and > doesn't do any substitutions. I tried a delayed assignment for eq but > it didn't work. What can I do? To force Mathematica to handle Derivatives properly you should use pure functions. So your rule should be: rule=f->(#^3&) Gruss Peter -- ==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-== Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de