Need Help With Locator in a Manipulate

• To: mathgroup at smc.vnet.net
• Subject: [mg132261] Need Help With Locator in a Manipulate
• From: Gregory Lypny <gregory.lypny at videotron.ca>
• Date: Sun, 26 Jan 2014 03:14:21 -0500 (EST)
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• Delivered-to: l-mathgroup@wolfram.com
• Delivered-to: mathgroup-outx@smc.vnet.net
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```Hello everyone,

I'm creating a Manipulate that has two locators. I was able to get the first locator, pt1, working the way I want, but am not sure how to handle the second, pt2.

Locator pt1 determines the intersection of two curves, a straight line with slope m and a power function, k[], with shape parameter a. Both m and a can be varied using sliders. I want the second locator, pt2, to be constrained to move along the line determined by locator pt1 and slope m. In a previous post some time ago, Bob Hanlon and John Fultz kindly showed me how to constrain a locator to move around the perimeter of a circle, but this used DynamicModule, and I am not sure how to bring this into a Manipulate. Any guidance would be greatly appreciated.  The code for my Manipulate is below. Right now, locator pt2 is arbitrarily set to {50,50} but it doesn't do anything.

Manipulate[
Module[{f,b,xmin=0,xmax=100,k},
b=pt1[[2]]-m*pt1[[1]];
k[{x_,y_},a_]:=x^a y^(1-a);
Plot[{(k[pt1,a]/x^a)^(1/(1-a)),m x +b},{x,0,100},
AxesOrigin->{0,0},
PlotRange->{Automatic,{0,200}}]],
{{a,.5,"Shape (a)"},.2,.8,Appearance->"Labeled"},
{{m,-1,"Slope (m)"},-3,-.4,Appearance->"Labeled"},
{{pt1,{10,80}},Locator},
{{pt2,{50,50}},Locator}]

Regards,

Gregory Lypny

```

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