Re: how to replace with definition
- To: mathgroup at smc.vnet.net
- Subject: [mg123722] Re: how to replace with definition
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Fri, 16 Dec 2011 05:52:29 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
On 12/15/11 at 4:53 AM, radford.schantz at mms.gov (r_poetic) wrote: >Hello, I can't seem to manage this replacement: >k[t] = A[t]/L[t]; >L'[t] = lambda L[t]; A'[t] = s k[t]^alpha; >D[k[t],t] >output= lambda A[t] + s (A[t]/L[t]) ^ alpha >----------------- ----------------------------- >L[t] L[t] >How can the ratio A[t]/L[t] be replaced with k[t] here? I have >tried a number of possibilities using /. or Replace. You have defined k[t] to be A[t]/L[t] by using Set (=). So, since Mathematica by default will evaluate everything it can, immediately after replacing anything with k[t], Mathematica will evaluate k[t] to A[t]/L[t]. That is, there is no way to get A[t]/L[t] to become k[t] unless you do something to prevent Mathematica from evaluating k[t] using Hold or something equivalent. Best, if you want the end expression to have k[t] simply don't define k[t] to be something using Set.