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

```

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