Re: evaluations in Plot in Manipulate?

*To*: mathgroup at smc.vnet.net*Subject*: [mg91033] Re: evaluations in Plot in Manipulate?*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Mon, 4 Aug 2008 03:23:19 -0400 (EDT)*Organization*: Uni Leipzig*References*: <g6kc15$k4d$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de

Hi, you miss, that Manipulate[] by default localize the variables and in expr=Exp[a] Manipulate[ Exp[a],{a,1,5}] a in expr is not the same as "a" in Manipulate[]. You can see this when you type Manipulate[HoldForm[a], {a, 1, 5}] The option LocalizeVariables control the generation of local variables. Regards Jens J Davis wrote: > I must be overlooking something simple in the way Mathematica handles > the arguments of Manipulate. > > Could someone expound on the contrast in behavior between the last > example below and the previous two? > > Clear[a, b, c, h]; > a = 1; > c = 1; > h[t_] = InverseLaplaceTransform[1/(a s^2 + b s + c), s, t] > > > Manipulate[ > Plot[Evaluate[ > InverseLaplaceTransform[1/(a s^2 + b s + c), s, t]], {t, 0, 10}, > PlotRange -> {{0, 10}, {-1, 1}}], {b, 0, 5}] > > (* works fine *) > > > Manipulate[ > Plot[-((E^((-(b/(2 a)) - Sqrt[b^2 - 4 a c]/(2 a)) t) - > E^((-(b/(2 a)) + Sqrt[b^2 - 4 a c]/(2 a)) t))/Sqrt[ > b^2 - 4 a c]), {t, 0, 10}, PlotRange -> {{0, 10}, {-1, 1}}], {b, 0, > 5}] > > (* works fine... I just copied and pasted the output of h[t] into the > Plot[...] *) > > > Manipulate[ > Plot[Evaluate[h[t]], {t, 0, 10}, > PlotRange -> {{0, 10}, {-1, 1}}], {b, 0, 5}] > > (* nothing... what am I missing? *) > > Doesn't Evaluate[h[t]] hold the evaluated form of h[t] (so that it is > computed just once) and then Plot simply substitutes a sequence of > numerical values into that evaluated form? If so, why is there no > output? > > Thanks in advance, > John >