Chop?

*To*: mathgroup at smc.vnet.net*Subject*: [mg23007] Chop?*From*: Russell Towle <rustybel at foothill.net>*Date*: Tue, 11 Apr 2000 23:18:26 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

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

**Follow-Ups**:**RE: Chop? Programming Challenge!!***From:*Russell Towle <rustybel@foothill.net>