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Re: Re: Locator question

• To: mathgroup at smc.vnet.net
• Subject: [mg79327] Re: [mg79292] Re: [mg79272] Locator question
• From: Murray Eisenberg <murray at math.umass.edu>
• Date: Wed, 25 Jul 2007 01:57:59 -0400 (EDT)
• Organization: Mathematics & Statistics, Univ. of Mass./Amherst
• References: <2851721.1185180232088.JavaMail.root@m35> <200707240956.FAA25082@smc.vnet.net>
• Reply-to: murray at math.umass.edu

The Locator is NOT tracking along the curve.  That is, it is not 
constrained to be on the curve. The locator can be at any ({x,y} in the 
figure, although the point of tangency is, of course, constrained to lie 
on the curve plotted.

DrMajorBob wrote:
> How's this?
> 
> Manipulate[
>   Show[
>    Plot[g[x], {x, 0, 2 \[Pi]}],
>    p[[2]] = g@p[[1]]; slope = D[g[x], x] /. x -> p[[1]];
>    Plot[p[[2]] + slope (x - p[[1]]), {x, 0, 2 \[Pi]}],
>    PlotLabel ->
>     Style["slope of f(x)= " <>
>       ToString[NumberForm[slope, {6, 4}]]]], {{g, Sin,
>     "function"}, {Sin -> TraditionalForm[Sin[x]],
>     Cos -> TraditionalForm[Cos[x]], #^2 & -> TraditionalForm[x^2]},
>    ControlType -> PopupMenu}, {{p, {0, 0}}, Locator}]
> 
> Bobby
> 
> On Mon, 23 Jul 2007 02:40:52 -0500, Mike <mjp.1 at comcast.net> wrote:
> 
>> All,
>>
>> I'm trying to get the locator to track a point along a given curve:
>>
>>
>> bothfandtan[g_, p_] :=
>>  Module[{f = g,
>>    eqline = (D[g, x] /. x -> p[[1]]) (x - p[[1]]) + p[[2]]},
>>   Show[{Plot[f, {x, 0, 2 \[Pi]}], Plot[eqline, {x, 0, 2 \[Pi]}]}]]
>>
>> Manipulate[
>>  Show[bothfandtan[g, p],
>>   PlotLabel ->
>>    Style["slope of f(x)= " <>
>>      ToString[NumberForm[D[g, x] /. x -> p[[1]], {6, 4}]]]],
>>  {{g, Sin[x], "function"},
>>   {Sin[x] -> TraditionalForm[Sin[x]],
>>    Cos[x] -> TraditionalForm[Cos[x]],
>>    x^2 -> TraditionalForm[x^2]}}, {{p, {0, 0}}, Locator},
>>  SaveDefinitions -> True]
>>
>>
>> I've tried a number of possibilities, but I can't seem to get this to 
>> work. Mathematica's help section on this isn't very helpful.
>>
>> Thanks for the help...
>>
>> Mike
>>
>>
> 
> 
> 

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305

• References:
  • Re: Locator question
    • From: DrMajorBob <drmajorbob@bigfoot.com>