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Re: newbie: can't Manipulate ListPlot of recurrence

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96818] Re: newbie: can't Manipulate ListPlot of recurrence
  • From: Albert Retey <awnl at gmx-topmail.de>
  • Date: Wed, 25 Feb 2009 04:07:14 -0500 (EST)
  • References: <go0j40$n0f$1@smc.vnet.net>

Tom Roche wrote:
> summary: I'm trying to Manipulate the logistic map. I can ListPlot it,
> but when I try to Manipulate, the UI behaves weirdly.
> 
> details:
> 
> As advertised by the Subject:, I'm new to Mathematica (specifically
> 7.0.0 for Students for 32-bit Windows on XP Pro) so please excuse any
> lapses in terminology. I'd also appreciate pointers to specific docs
> rather than just an RTFM.
> 
> I'm trying to model the logistic map y=a y (1-y):
> 
> http://en.wikipedia.org/wiki/Logistic_map
> http://mathworld.wolfram.com/LogisticMap.html
> http://www.phy.duke.edu/~palmer/notebooks/LogisticMap.nb
> 
> To start with I just tried to plot it, which works:
> 
> Clear[a, y];
> a=3.5;
> y=0.4;
> ListPlot[Table[y=a y (1-y),{50}],Joined->True]
> 
> I'd like to Manipulate a and y, but when I try to
> 
> Clear[a, y];
> Manipulate[
>   ListPlot[Table[y=a y (1-y),{50}],Joined->True], {{a, 3.5}, 0,  4},
> {{y, 0.4}, 0, 1}]
> 
> I get weird behavior:
> 
> 1 initially the y slider oscillates
> 
> 2 initially the plot displays but flashes (apparently between two
>   phases) until I click one of the sliders
> 
> 3 the y slider will not move
> 
> 4 the a slider can be dragged, but to no effect (i.e. the plot does
>   not change)

all these come from the fact that you are asigning to y which is one of
the variables that you want to manipulate, which is almost never a good
idea...

> 5 there are no error messages


> What am I doing wrong? and how can I Manipulate this map?

I think this does what you want:

Clear[a, y];
Manipulate[
 ListPlot[
  Block[{x = y},
   Table[x = a x (1 - x), {50}]
   ],
  Joined -> True, PlotRange -> {0, 1}
  ],
 {{a, 3.5}, 0, 4},
 {{y, 0.4}, 0, 1}
 ]

hth,

albert


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