Constrain locator

*To*: mathgroup at smc.vnet.net*Subject*: [mg121706] Constrain locator*From*: Tom De Vries <tidetabletom at gmail.com>*Date*: Mon, 26 Sep 2011 20:05:30 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Hello everyone, I'm looking for a simple way to constrain a locator to a particular function. I've seen a few methods given by posters to this group and others. In programs like Sketchpad and Geogebra you can add a point to a function and immediately constrain the point to that function. You can then "trace" the point, displaying coordinates, etc. I'm trying to work within Mathematica if I can, but this is hard for me to implement. Working through a few examples, I distilled things down to the following snippet of code. It puts a point on the function y = x^2 and allows the point to be dragged along it. f0[x_] := x^2; DynamicModule[{p = {1, 1}}, loc := Locator[Dynamic[p, (p = {#[[1]], f0[#[[1]]]}) &]]; Show[{Plot[f0[x], {x, -10, 10}], Graphics[{loc}]}, PlotRange -> {{-4, 4}, {-1, 10}}, AspectRatio -> 1] ] I would be grateful for a few things... A) a little help on exactly how this works...! B) changing the display of the locator to a point on the function C) displaying the coordinate of the point I appreciate the input given by members of this group. Sorry for the trivial question, but it sure would help with a lot of things I am trying to teach at the junior/high school level. Tom