Re: What is the point of having Initializations in DynamicModule and Manipulate?

*To*: mathgroup at smc.vnet.net*Subject*: [mg123047] Re: What is the point of having Initializations in DynamicModule and Manipulate?*From*: Gary <gpalmerlv at gmail.com>*Date*: Mon, 21 Nov 2011 04:29:49 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <398831.35647.1321702630679.JavaMail.root@m06> <jaal6b$13n$1@smc.vnet.net>

It is really nice to have these examples of variations. Would you explain for a rank beginner what is happening in the following snippet from your last example? Dynamic@plot, Row[{"c: ", Slider[Dynamic[c, (c = #; calcAll[c]) &], {0, 1}, Appearance -> "Labeled"]}], That is, what is Dynamic@plot doing? Is it evaluating plot each time the slider is moved? What is the function of the @ symbol here in contrast with square brackets? And in Slider[Dynamic[c, (c = #; calcAll[c]) &], {0, 1},... what is going on in Dynamic[c, (c = #; calcAll[c]) &] ? Is # being instantiated with the values from the slider range? Why the ampersand? Gary On Nov 20, 2:35 am, "David Park" <djmp... at comcast.net> wrote: > Mike (or is it Armand? Both nice.), > > I don't understand the purpose of the indicated display. Is the plot to be > completely static and just bundled with the dynamic part? In any case, for a > static plot: > > Module[{g, plot}, > g[x_] := Cos[x]; > plot := > Plot[g[x], {x, 1, 10}, > PlotRange -> {-1.1, 1.1}, > Frame -> True, > ImageSize -> 200]; > DynamicModule[{c = 0.5}, > {plot, Slider[Dynamic[c]], g[Dynamic@c]}] > ] > > For a case where the plot depends on c as a parameter we could use: > > DynamicModule[ > {c = 0.5, g, plot}, > g[x_] := Cos[x]; > plot[c_] := > Plot[g[c x], {x, 1, 10}, PlotRange -> {-1.1, 1.1}, Frame -> True, > ImageSize -> 300]; > Column[{ > Dynamic@plot[c], > Row[{"c: ", Slider[Dynamic[c], {0, 1}, Appearance -> "Labeled"]}] > }] > ] > > Here is a somewhat more interesting case where we calculate a dependent > dynamic variable, d, and then use that in making the plot. Here calcAll is > the routine that calculates the dependent quantities and it is called from > the second argument of Dynamic in the Slider. > > DynamicModule[ > {c = 0.5, d, g, plot, calcAll}, > g[x_] := Cos[x]; > > (* Calculate dependent dynamic variables *) > calcAll[cc_] := (d = cc^2; > plot = Plot[g[d x], {x, 1, 10}, PlotRange -> {-1.1, 1.1}, > Frame -> True, > ImageSize -> 300]); > > (* Initialize *) > calcAll[c]; > > (* Display *) > Column[{ > Dynamic@plot, > Row[{"c: ", > Slider[Dynamic[c, (c = #; calcAll[c]) &], {0, 1}, > Appearance -> "Labeled"]}], > Dynamic@Row[{"d: ", d}] > }] > ] > > To me, this just seems to be more intuitive, although perhaps a bit more > wordy. And it works. > > David Park > djmp... at comcast.nethttp://home.comcast.net/~djmpark/ > > From: Armand Tamzarian [mailto:mike.honeychu... at gmail.com] > > I'd be interested in feedback from other users about the way in which > Initializations works within DynamicModule (and Manipulate?). It is > fair to say that I expected an initialization to occur "initially." > That is to say I expected Initialization content to be evaluated prior > to the body of the DynamicModule. I have exchanged emails with tech > support about this. Attached is an example sent to me by tech support. > > ClearAll[plot, g]; > > (* and in a separate cell *) > DynamicModule[{c}, {plot, Slider[Dynamic[c]], g[Dynamic@c]}, > Initialization :> (g[x_] := Cos[x]; plot = Plot[g[x], {x, 1, 10}]), > UntrackedVariables -> {g}] > > It is important for this example to keep the ClearAll line in a > separate cell so that the global variables are only cleared once. On > my system (OS X 10.6.8, Mathematica 8.0.4) the output is a list > > {plot, "slider", g[0.]} > > where "slider" is the actual rendered slider but plot is the word > (unset variable) plot. In other words Global`plot has no value at the > time the body of the DynamicModule is evaluated. Ditto Global`g. > > If you evaluated the cell (the second cell with the DynamicModule) a > second time a plot graphic appears in the list and g[0.] becomes > Cos[0.]. This is not surprising because Global`plot and Global`g now > have a value. > > Wolfram have indicated that this is working as designed -- which is > presumably why this example was sent to me of how this should work. If > that is the case it seems poorly designed because (and it is here I > would like feedback) users would expect initializations to be > evaluated prior to the body of the DynamicModule -- otherwise what is > the point? > > I'd appreciate the thoughts of other users about this. > > Additionally I have been told by Wolfram that wrapping Dynamic around > the variable(s) that are not being evaluated will trigger the > evaluation. But why would a user want to make plot or g Dynamic? It > seems to me that the entire purpose of having an Initialization is to > evaluate this "one off" variable/functions. > > thanks > > Mike

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