Re: About the error message Indeterminate

• To: mathgroup at smc.vnet.net
• Subject: [mg91381] Re: About the error message Indeterminate
• From: MarvelousTau <nightvista at gmail.com>
• Date: Tue, 19 Aug 2008 07:15:12 -0400 (EDT)
• References: <g88v76\$guj\$1@smc.vnet.net> <g8b8ua\$8qd\$1@smc.vnet.net>

```Thanks. Really.

On Aug 18, 3:38 pm, Jens-Peer Kuska <ku... at informatik.uni-leipzig.de>
wrote:
> Hi,
>
> try ArcTan[x,y] instead of ArcTan[y/x]
>
> Regards
>    Jens
>
> MarvelousTau wrote:
> > I think you all might have been check the example the bouncer in the
> > entry Dynamic. But it is on a flat ground. So I want to make some
> > change to let it bounce on hills, which formed by Sine function. The
> > collisional consummation and reflection angle have been taken
> > considered, but when the point touches the ground, it doesn't move any
> > longer and the velocity shows indeterminate. I know indeterminate
> > means such an issue like 0/0, but I replace my reflecting function
> > with the colliding position and get a certain answer. I don't know if
> > is there any other issues will cause indeterminate.
>
> > Anyway, check the code first.
>
> > function[x_] := Sin[x] + 0.5 Sin[6 x];
> > Reflection[{{x_, y_}, {vx_, vy_}}] := {{x, y},
> >   0.8 Sqrt[vx^2 + vy^2] {Cos[2 ArcTan[function'[x]] - ArcTan[vy/vx]],
> >     Sin[2 ArcTan[function'[x]] - ArcTan[vy/vx]]}}
>
> > (* where function[] means the ground and Reflection[] shows how the
> > ball bounces up, where x, y means position and vx, vy means velocity.
> > 0.8 Is the consummation of collision, Sqrt is the norm of speed and
> > the latter stuff is the new velocity in x and y direction. *)
>
> > PointSet = {{4, 6}, {0, -0.01}};
> > Plot[function[x], {x, -5, 5}, Axes -> None, Filling -> Bottom,
> >  PlotRange -> {{-5, 5}, {-2, 8}}, AspectRatio -> 1,
> >  Epilog ->
> >   Point[Dynamic[
> >     PointSet =
> >      If[PointSet[[1, 2]] >=
> >        function[PointSet[[1, 1]]], {PointSet[[1]] + PointSet[[2=
]],
> >        PointSet[[2]] + {0, -0.001}}, Reflection[PointSet]];
> >     PointSet[[1]]]]]
> > Dynamic[PointSet]
>
> > (*I used Epilog to draw the point. I didn't use Mouseclick because it
> > will cause a dump*)
>
> > I'll keep waiting here and thanks in advance.
>
> > Tao Yue

```

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