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Locator question

• To: mathgroup at smc.vnet.net
• Subject: [mg79272] Locator question
• From: Mike <mjp.1 at comcast.net>
• Date: Mon, 23 Jul 2007 03:40:52 -0400 (EDT)

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