Re: Chop?

*To*: mathgroup at smc.vnet.net*Subject*: [mg23034] Re: Chop?*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Thu, 13 Apr 2000 02:43:22 -0400 (EDT)*Organization*: Universitaet Leipzig*References*: <8d0prj$4g9@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, what is with $tiny = 1.0*10^(-5); SetAttributes[myChop, Listable] myChop[x_] := Module[{xx}, xx = Chop[x]; If[Abs[xx] < $tiny, 0., xx]] It is not perfect, because it does not change expressions like myFunction[0.00000006] but I hope it helps for your vectors Regards Jens Russell Towle wrote: > > Hi, > > I have been noticing lately that sometimes Chop does not succeed in > reducing numbers close to 0 to 0. Although my email program scrambled the > superscripts, those '-7's down there are from the 10^-7's where I would > expect (and would want) to see plain 0. Mathematica version 4.01 on a Mac. Copied > as plain text from OutputForm. > > This failure of Chop has ruined one of my most important algorithms, which > takes the Union of a list of n-vectors. It has wrecked in turn my most > important notebooks. Notice, if you will, members 5 and 6 of the list > below, where the z component should have Chopped to zero, but instead is > two very small numbers of opposite sign. > > In[221]:= > Chop[q2] > > Out[221]= > {{-0.707107, -1., 0}, {-0.707107, 0, -1.}, {-0.707107, 0, 1.}, {-0.707107, > 1., 0}, > > -7 -7 > {-0.707107, -1., -1.11022 10 }, {-0.707107, -1., 1.11022 10 }, > > -7 -7 > {-0.707107, 1.11022 10 , -1.}, {-0.707107, 1., 1.11022 10 }, > {-0.707107, -1., 0}, > > {-0.707107, 0, -1.}, {-0.707107, 0, 1.}, {-0.707107, 1., 0}, {0.707107, > -1., 0}, > > {0.707107, 0, -1.}, {0.707107, 0, 1.}, {0.707107, 1., 0}, > > -7 -7 > {0.707107, -1., -1.11022 10 }, {0.707107, -1., 1.11022 10 }, > > -7 -7 > {0.707107, 1.11022 10 , -1.}, {0.707107, 1., 1.11022 10 }} > > Russell Towle > Box 141 > Dutch Flat, CA 95714 > (530) 389-2872