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MathGroup Archive 2000

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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




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