Re: Annoying Little Problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg24870] Re: Annoying Little Problem*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Sat, 19 Aug 2000 04:45:46 -0400 (EDT)*References*: <8mdm1e$5li@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Clear[v2] v2 = {4, 0, -6} N[Sqrt[v2.v2], 3] 7.2111 N is concerned with output and its precision not with how the output is displayed. For the latter we can use NumberForm NumberForm[N[Sqrt[v2.v2]], 3] (*1*) "7.21" The output is the underlying decimal. % 7.2111 And even this is the display of a stored number with 16 decimal places We can see the situation if we look at the cell expression of the output from (*1*); which is (using Format>ShowExpression) Cell[BoxData[ TagBox[ InterpretationBox["\<\"7.21\"\>", 7.2111025509279782, AutoDelete->True], (NumberForm[ #, 3]&)]], "Output", CellLabel->"Out[132]//NumberForm="] -- Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565 "Nalanji Dreaming" <ayrton at rac1.wam.umd.edu> wrote in message news:8mdm1e$5li at smc.vnet.net... > I'm having an annoying little problem with version 4.0.1.0. I wrote the > following info in a notebook and ran it: > > Clear[v2] > v2 = {4, 0, -6} > N[Sqrt[v2.v2]] > N[Sqrt[v2.v2], 3] > > Now the third line gives me 7.2111 but the fourth line gives me the > same instead of 7.21. Does anyone have any idea what may be the problem? > Am I doing something wrong? > > thanks, > Nalanji Dreaming >