Re: Grouping terms under the radical

*To*: mathgroup at smc.vnet.net*Subject*: [mg120106] Re: Grouping terms under the radical*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Fri, 8 Jul 2011 04:54:50 -0400 (EDT)*Reply-to*: hanlonr at cox.net

You could use $Post to apply the substitution to all output; however, ReleaseHold would not work without first clearing $Post since the substitution would be automatically reapplied to the output of the ReleaseHold. mySqrt = # /. Sqrt[x_]*Sqrt[y_] -> HoldForm[Sqrt[x*y]] &; $Post = mySqrt; expr = Sqrt[2 n] HoldForm[Sqrt[2*n]] $Post =. expr // ReleaseHold Sqrt[2]*Sqrt[n] Perhaps easier to just apply mySqrt as required. expr // mySqrt HoldForm[Sqrt[2*n]] Bob Hanlon ---- Paul von Hippel <paulvonhippel at yahoo.com> wrote: ============= Thanks for this solution! But what if the expression Sqrt[2*n] is not something that I've input, but part of an expression in Mathematica's output. The output shows 2 and n under separate radicals. How can I tell the software I prefer to see terms combined under a common radical? --- On Thu, 7/7/11, Bob Hanlon <hanlonr at cox.net> wrote: From: Bob Hanlon <hanlonr at cox.net> Subject: [mg120106] Re: Grouping terms under the radical To: "paulvonhippel at yahoo" <paulvonhippel at yahoo.com>, mathgroup at smc.vnet.net Date: Thursday, July 7, 2011, 7:25 AM expr = Sqrt[2*n] Sqrt[2]*Sqrt[n] expr /. Sqrt[x_] Sqrt[y_] -> HoldForm[Sqrt[x*y]] HoldForm[Sqrt[2*n]] % // ReleaseHold Sqrt[2]*Sqrt[n] Bob Hanlon ---- paulvonhippel at yahoo <paulvonhippel at yahoo.com> wrote: ============= This must be a classic question. When I input Sqrt[(2 n)] Mathematica displays the output as Sqrt[2] Sqrt[n] -- i.e., both 2 and n are under their own radical. The display of output doesn't change if I impose the assumption that n > 0. This is fine from a mathematical point of view, but it looks unconventional when pasted into a paper. It seems to me most authors would keep the 2 and the n under a common radical -- how can I get Mathematica to do the same? Thanks!