Re: Need Help With Locator in a Manipulate

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• Subject: [mg132272] Re: Need Help With Locator in a Manipulate
• From: Gregory Lypny <gregory.lypny at videotron.ca>
• Date: Tue, 28 Jan 2014 06:15:43 -0500 (EST)
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```Excellent. Thank you, Bob.

Late yesterday I had accomplished, more or less, the same thing by putting the following in the Epilog of my plot:

Locator[Dynamic[pt2, pt2 = {pt2[[1]], m pt2[[1]] + pt1[[2]] - m*pt1[[1]]}]]

In either case, the locator jiggles as it is being moved. I suppose this because its position is being re-evaluated. Is there any way to make its movement smoother?

Regards,

Gregory

On Sun, Jan 26, 2014, at 2:05 PM, Bob Hanlon <hanlonr357 at gmail.com> wrote:

> Reposition the locator point each time the locator is moved.
>
> Manipulate[
>  Module[{f, b, xmin = 0, xmax = 100, k},
>   b = pt1[[2]] - m*pt1[[1]];
>   k[{x_, y_}, a_] := x^a y^(1 - a);
>
>   pt2 = {#[[1]], m #[[1]] + b} &[pt2];
>
>   Plot[{(k[pt1, a]/x^a)^(1/(1 - a)), m x + b},
>    {x, 0, 100},
>    AxesOrigin -> {0, 0},
>    PlotRange -> {{xmin, xmax}, {Automatic, 200}}]],
>  {{a, .5, "Shape (a)"}, .2, .8, .01,
>   Appearance -> "Labeled"},
>  {{m, -1, "Slope (m)"}, -3, -.4, .01,
>   Appearance -> "Labeled"},
>  {{pt1, {10, 80}}, Locator},
>  {{pt2, {50, 50}}, Locator}]
>
>
> Bob Hanlon
>
>
>
> On Sun, Jan 26, 2014 at 3:14 AM, Gregory Lypny <gregory.lypny at videotron.ca> wrote:
>
> 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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