Re: Manipulate a Plot of Evaluate DSolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg127500] Re: Manipulate a Plot of Evaluate DSolve*From*: Juan Barandiaran <barandiaran.juan at gmail.com>*Date*: Mon, 30 Jul 2012 03:46:44 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*References*: <20120729070521.C7CB3684D@smc.vnet.net> <CAEtRDSfuzxN12HoeTLPuZGmegBOpubxd3J_g0ESgnT8=KQStBw@mail.gmail.com>

Thanks for your answer Bob, Of course your solution works, but I still don't understand why mine doesn't and I cannot use your proposed approach because the way you write the problem it is easy for Mathematica to solve the DSolve. And this is just a simple example, in my real problem the DSolve cannot be solved analytically. This is why I tried to express the function as: {{y -> Function[{x}, DSolve[y'[x] == Cos[coef *x], y, x]]}} , which is something like the output I get from my DSolve. Thanks for your help. Juan 2012/7/29 Bob Hanlon <hanlonr357 at gmail.com> > Clear[func]; > > func[coef_, c_, x_] = > y[x] /. DSolve[{y'[x] == Cos[coef*x], y[0] == c}, y[x], x][[1]] // > Simplify > > c + Sin[coef*x]/coef > > > Manipulate[Plot[Evaluate[ > func[coef, c, x] /. > c -> Range[5]], > {x, -10, 10}, > PlotRange -> {-5, 10}], > {{coef, 1}, 0.1, 5, 0.01, > Appearance -> "Labeled"}] > > > Bob Hanlon > > > On Sun, Jul 29, 2012 at 3:05 AM, <barandiaran.juan at gmail.com> wrote: > > Hi, > > > > I'm trying to Manipulate a Plot of a quite difficult function which > involves solving a differential equation, but cannot be solved analytically. > > > > To try to simplify the example and simulate it, let's assume that we > have the following function: > > > > func[coef_] = {{y -> Function[{x}, DSolve[y'[x] == Cos[coef *x], y, x]]}} > > > > Manipulate[Plot[{{Evaluate[y[x] /. func[coef] /. C[1] -> {Range[-5, > 0]}]}}, {x, -10, 10}], {{coef , 1}, 0.1, 5}] > > > > I get an error: DSolve::dsvar: "-9.99959 cannot be used as a variable" > > > > I think that this is because Manipulate assigns a value to x (= > -9.99959) BEFORE solving the DSolve, even though to avoid it I'm using the > Evaluate function, which should process the function before assigning a > value to x. > > > > But the thing is that the "coef" to be Manipulated is at the same > "level" as the x in the Manipulate block, so probably if I need the coef to > solve the DSolve, I also have the x that gives me an error. > > > > Is there any workaround? I guess I'm not understanding properly how > Mathematica processes these simple expressions. > > > > Thanks, Juan > > >

**References**:**Manipulate a Plot of Evaluate DSolve***From:*barandiaran.juan@gmail.com