Re: Delayed Derivative Operator

*To*: mathgroup at smc.vnet.net*Subject*: [mg81816] Re: [mg81762] Delayed Derivative Operator*From*: Curtis Osterhoudt <cfo at lanl.gov>*Date*: Thu, 4 Oct 2007 04:21:37 -0400 (EDT)*Organization*: LANL*References*: <200710030626.CAA28793@smc.vnet.net>*Reply-to*: cfo at lanl.gov

On Wednesday 03 October 2007 00:26:48 ToddSmith wrote: > 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? > > -Thanks Maybe eq := Hold[D[f[x], x] == 5]; rule = f[x] -> x^3; In[7]:= ReleaseHold[eq /. rule] Out[7]= 3 x^2 == 5 will do what you want. -- ========================================================== Curtis Osterhoudt cfo at remove_this.lanl.and_this.gov PGP Key ID: 0x4DCA2A10 Please avoid sending me Word or PowerPoint attachments See http://www.gnu.org/philosophy/no-word-attachments.html ==========================================================

**References**:**Delayed Derivative Operator***From:*ToddSmith <elliptic1@gmail.com>