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Re: DynamicModule question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88611] Re: DynamicModule question
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Fri, 9 May 2008 07:17:53 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fvudm6$eb5$1@smc.vnet.net>

J. McKenzie Alexander wrote:

> Can someone please explain to me why the following happens?  It's a  
> silly little example to illustrate a problem I ran into recently...
> 
> First, evaluate the following in separate cells:
> 
> 	Needs["PieCharts`"];
> 
> 	data = {.25, .75}
> 
> Then evaluate the following:
> 
> 	DynamicModule[{size = 300},
> 	 Column[{
> 	   Slider[Dynamic[size], {100, 500}],
> 	   Dynamic[PieChart[data, ImageSize -> size]]
> 	   }]
> 	 ]
> 
> Notice that you can not only resize the graphic by  dragging the  
> slider, but if you change the definition of data, that's reflected  
> automatically in the graphic as well.
> 
> However, suppose you wrap the DynamicModule in a function like so:
> 
> 	foo[data_] := DynamicModule[{size = 300},
> 	  Column[{
> 	    Slider[Dynamic[size], {100, 500}],
> 	    Dynamic@PieChart[data, ImageSize -> size]
> 	    }]
> 	  ]
> 
> Now evaluate
> 
> 	foo[ data ]
> 
> If you change the definition of data in the notebook, the second  
> DynamicModule doesn't update the pie charts. I don't understand what  
> breaks when you wrap the DynamicModule in a function definition.

Try

     Dynamic@foo[data]

Now, why Dynamic is needed here? I do not know. Looking at the 
expressions in the output cells (Shift + Cmd + E ) for the code 
generated by entering directly the DynamicModule or by using a function 
both resulting expressions look very similar (even identical, as far as 
I can trust my sight :-)

Regards,
-- Jean-Marc


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