       Re: Constraining a Location to Move Along a Plot in a Manipulate

• To: mathgroup at smc.vnet.net
• Subject: [mg127779] Re: Constraining a Location to Move Along a Plot in a Manipulate
• From: Bob Hanlon <hanlonr357 at gmail.com>
• Date: Wed, 22 Aug 2012 02:25:19 -0400 (EDT)
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• References: <20120821013043.F31B7684F@smc.vnet.net>

```Manipulate[
Module[{f, m, b, xmin = -5, xmax = 5},
f[x_] :=
(m*x + b /. Solve[{
pt1[] == m*pt1[] + b,
pt2[] == m*pt2[] + b},
{m, b}][]);
Graphics[{
Line[{{xmin, f[xmin]},
{xmax, f[xmax]}}],
AbsolutePointSize,
Red,
Tooltip[Point[{x, f[x]}], {x, f[x]}],
Blue,
Tooltip[Point[
{InverseFunction[f][y], y}],
{InverseFunction[f][y], y}]},
Frame -> True, Axes -> False,
PlotRange -> {{xmin, xmax}, {-5, 5}}]],
{{x, -1, Style["x", Red, Bold, 12]}, -5, 5, 0.1,
Appearance -> "Labeled"},
{{y, 1, Style["y", Blue, Bold, 12]}, -5, 5, 0.1,
Appearance -> "Labeled"},
{{pt1, {-4, -4}}, Locator},
{{pt2, {4, 4}}, Locator}]

Bob Hanlon

On Mon, Aug 20, 2012 at 9:30 PM, Gregory Lypny
<gregory.lypny at videotron.ca> wrote:
> Hello everyone,
>
> Awhile back, participants on this forum kindly showed me how to constrain a locator to move along a curve by using DynamicModule[...], an example of which is in the Help Centre.  But I can't figure out how to pull this off in a Manipulate,where I'm guessing that the locator would be a control.  Say I have a simple Manipulate that plots a line, y = mx + b, where m is control for changing the slope.  I would also like to have a locator that users can slide up and down the line in lieu of a slider control that draws a point on the line.
>
> Regards,
>
> Gregory
>

```

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