Re: Simple edit ...

*To*: mathgroup at smc.vnet.net*Subject*: [mg19329] Re: [mg19319] Simple edit ...*From*: "David Park" <djmp at earthlink.net>*Date*: Mon, 16 Aug 1999 02:14:58 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Michael Stokes wrote; >Consider the following examaple; > >z = (a+Sqrt[d+e])/(a Sqrt[d+e]) > >z //. Sqrt[d+e] ->L > >The replacement function only replaces the instance of Sqrt[d+e] in the >numerator and leaves the instance in the denominator alone. Why does >this not work and what is the work around? > >Regards, >Mike > Mike, This is a very common error. Look at the FullForm of z. FullForm[z] Times[Power[a, -1], Power[Plus[d, e], Rational[-1, 2]], Plus[a, Power[Plus[d, e], Rational[1, 2]]]] The expression in the denominator that you wish to match is actually of the form Power[Plus[d, e], Rational[-1, 2]] and Power[Plus[d, e], Rational[1, 2]] does not match it. This would work: z /. Power[d + e, Rational[n_, 2]] -> L^n (a + L)/(a*L) Item in the denominator always require care when matching with rules. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/