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Re: Dynamic changing of variables

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96370] Re: Dynamic changing of variables
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Thu, 12 Feb 2009 06:38:52 -0500 (EST)
  • References: <gmu8rl$gn3$1@smc.vnet.net>

The problem of updating a lies with its invisible dependence on b. If
you make it explicitely dependent on b you can drop the first dynamic
and a is not wrapped and can be used for calculations.

DynamicModule[{a, b = 0},
a[b_] = Sin[b];
 Column[{Dynamic[a[b]], Slider[Dynamic[b], {0, 2*Pi}]}]]

Alternatively, you could have wrapped the whole assignment with
Dynamic:

DynamicModule[{a, b = 0},
 Column[{Dynamic[a = Sin[b]], Dynamic[a + 1],
   Slider[Dynamic[b], {0, 2*Pi}]}]]

Cheers -- Sjoerd

On Feb 11, 12:21 pm, Patrick Scheibe <psche... at trm.uni-leipzig.de>
wrote:
> Hi,
>
> assume the following code lines:
>
> DynamicModule[{a, b = 0},
>   a = Dynamic[Sin[b]];
>   Column[{
>     Dynamic[a],
>     Slider[Dynamic[b], {0, 2*Pi}]
>    }]
> ]
>
> In order to update "a" with the actual value of Sin[b] I need
> Dynamic around it. Unfortunately, now the variable "a" is invisibly
> wrapped and completely useless for further calculations. I'm not able to
> calculate even a+1 inside the DynamicModule.
>
> DynamicModule[{a, b = 0},
>   a = Dynamic[Sin[b]];
>   Column[{
>     Dynamic[a+1],
>     Slider[Dynamic[b], {0, 2*Pi}]
>    }]
> ]
>
> If I'm not just too stupid and this behaviour is intended, then I'm
> wondering whether this doesn't lead to problems when you have more
> complex constructs with several dynamic variables.
>
> Cheers
> Patrick
>
> PS: I was just pointed by another person on this and I found a way
> around it. So cannot provide a real problem I'm having. Nevertheless, I
> would be glad to know what you think since I couldn't really find the
> point in the documentation where this is explained.



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