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Topic: Chop?
Replies: 2   Last Post: Apr 13, 2000 11:38 AM

 Messages: [ Previous | Next ]
 Russell Towle Posts: 70 Registered: 12/3/04
Chop?
Posted: Apr 11, 2000 11:17 PM

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

Date Subject Author
4/11/00 Russell Towle
4/13/00 Jens-Peer Kuska
4/13/00 Kevin J. McCann