Re: Derivatives in replacement rules
- To: mathgroup at smc.vnet.net
- Subject: [mg125776] Re: Derivatives in replacement rules
- From: Rodrigo Murta <murta at rodrigomurta.com>
- Date: Mon, 2 Apr 2012 04:22:48 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <jl3v1b$3mi$1@smc.vnet.net>
On Mar 30, 6:39 am, Yi Wang <tririverwan... at gmail.com> wrote: > Hi, all, > > When I am using the following replacement rule: > > b[t] c[t] a'[t] /. b_ a_'[t] -> D[b, t] > > I would expect to get D[b[t]c[t], t] = b'[t]c[t] + c'[t]b[t]. However, > I got 0 actually. To debug, when I set > > b[t] c[t] a'[t] /. b_ a_'[t] -> b > > I get b[t] c[t]. Thus pattern matching works and it appears D[b,t] > should be non-zero. > > Any ideas how I can get D[b[t]c[t], t] in the above pattern > replacement? Thanks! Hi Yi Use the dalayed rule :> instead of -> b[t] c[t] a'[t] /. x_ a_'[t] :> D[x, t] and you will get your expected result Best regards! Murta