Re: Re: Simplifying constants...bug?

*To*: mathgroup at smc.vnet.net*Subject*: [mg18590] Re: [mg18559] Re: [mg18489] Simplifying constants...bug?*From*: "Carl K.Woll" <carlw at fermi.phys.washington.edu>*Date*: Tue, 13 Jul 1999 01:01:25 -0400*Organization*: Department of Physics*References*: <7m3l22$shp@smc.vnet.net> <199907100618.CAA03008@smc.vnet.net.>*Sender*: owner-wri-mathgroup at wolfram.com

Alan, A tip for unraveling unexpected behavior: Look at the FullForm of an expression. In your case we find In[53]:= (a + c*d)/(c*d)//FullForm Out[53]//FullForm= Times[Power[c, -1], Power[d, -1], Plus[a, Times[c, d]]] So, we see that the c*d in the denominator has turned into c^-1 * d^-1. Hence, when the rule c*d->-z is applied, the denominator is left unaffected. You might try using a rule like c -> - z/d instead. Carl Woll Dept of Physics U of Washington calvitti at boes.ces.cwru.edu wrote: > here's some intersting behavior in 3.0: > > (a + c*d)/(b + c*d) //. c*d -> -z > > gives (as expected): > > (a - z)/(b - z) > > yet > > (a + c*d)/(c*d) //. c*d -> -z > > no longer simplifes the denominator: > > (a+b-z)/(c*d) > > anyone know why? > > +------------------------------------------+ > alan c > systems and control engineering > case western reserve university > > calvitti at alpha.ces.cwru.edu > +------------------------------------------+ > > "Ersek, Ted R" <ErsekTR at navair.navy.mil> writes: > > > Morten G. Dyndgaard wrote: > > ----------------------------- > > I am working with some annoyingly long equations that I want to simplify > > by including one set of parameters in a constant (or function) A, and > > another in B and so on. > > > > You can easily do: > > A = b+c+d+e > > > > but what I want to do is the reverse: > > b+c+d+e = A > > ----------------------------- > > > > This should help. > > In[1]:= > > expr=a+b+b1+c+c1+d+d1+e; > > > > > > In[2]:= > > expr/.a+b+c+d+e->A > > > > Out[2]= > > A+b1+c1+d1 > > > > > > Regards, > > Ted Ersek

**References**:**Re: Simplifying constants...bug?***From:*calvitti@boes.ces.cwru.edu