Re: how to test if 2 expressions are the same? Mathematica 5.0

*To*: mathgroup at smc.vnet.net*Subject*: [mg46104] Re: how to test if 2 expressions are the same? Mathematica 5.0*From*: drbob at bigfoot.com (Bobby R. Treat)*Date*: Fri, 6 Feb 2004 04:15:27 -0500 (EST)*References*: <bvt135$oj5$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

I'd think all these would work; some do and some don't: expr = 1 - Sin[x]^2 == Cos[x]^2; simplifiers = {Simplify, FullSimplify, TrigExpand, TrigReduce, TrigToExp}; Through[Compose[simplifiers, expr]] {True, True, 1 - Sin[x]^2 == Cos[x]^2, 1 - Sin[x]^2 == Cos[x]^2, True} The results for Log, on the other hand, don't surprise me. Simplify and FullSimplify (correctly) do not assume that x is a positive real, et cetera. PowerExpand does make that kind of assumption. expr = a*Log[x] == Log[x^a]; simplifiers = {Simplify, FullSimplify, PowerExpand}; Through[Compose[simplifiers, expr]] {a*Log[x] == Log[x^a], a*Log[x] == Log[x^a], True} Sometimes subtracting may work when Equal doesn't (but not this time): expr = a*Log[x] - Log[x^a]; simplifiers = {Simplify, FullSimplify, PowerExpand}; Through[Compose[simplifiers, expr]] {a*Log[x] - Log[x^a], a*Log[x] - Log[x^a], 0} Bobby nma124 at hotmail.com (steve_H) wrote in message news:<bvt135$oj5$1 at smc.vnet.net>... > hello; > > I am confused. > > many times, I want to find if there is a way to obtain one expression > from another by tranformation. > > for example, we know that 1-sin^2(x) = cos^2(x), and a*log(x)=log(x^a), > etc.., but sometimes this does not seem to work using SameQ: > > SameQ[a Log[x], Log[x^a] ] > False > > I tried MatchQ and that also gives False. > > what is the right way to do these things in Mathematica? I checked the on-line help, > and can't seem to see the right command for this. > > many thanks, > STeve