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MathGroup Archive 2005

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Re: "Null" appearing in exported gif

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63425] Re: "Null" appearing in exported gif
  • From: "Norbert Marxer" <marxer at mec.li>
  • Date: Fri, 30 Dec 2005 04:43:50 -0500 (EST)
  • References: <dp05m6$g63$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hello

You get a Null in your graphics, because Table produces the following
list:

{{-Graphics-,Null},{-Graphics-,Null},...}

This happens because your command has (essentially) the following
structure:

bFwd=Table[{
      ...;DisplayTogether[...],
      pastSymbol=prevSymbol;prevSymbol=currSymbol;
      },
    {t,0,5-stepsize,stepsize}]

Because of the comma after DisplayTogether you get 2 items for each
element of the list (i.e. a list of pairs): the fist element is the
graphics object (from DisplayTogether), the second is the Null (because
of the semicolon after currSymbol).

To get rid of the Null, you can modify the input in the following way:

1. use the symbol gr to store the graphics

2. replace the comma after DisplayTogether with a semicolon

3. insert the symbol gr after "currSymbol;"

4. optional: you can eliminate the curly brackets of
Table[{...},{...}]: i.e. Table[...,{...}]

bFwd=Table[{
      ...;gr=DisplayTogether[...];
        pastSymbol=prevSymbol;prevSymbol=currSymbol;
        gr
      },
    {t,0,5-stepsize,stepsize}]

With these modifications everything works nicely.

Best regards
Norbert Marxer
www.mec.li


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