Re: Re: Locator question
- To: mathgroup at smc.vnet.net
- Subject: [mg79452] Re: [mg79433] Re: Locator question
- From: Murray Eisenberg <murray at math.umass.edu>
- Date: Fri, 27 Jul 2007 05:48:07 -0400 (EDT)
- Organization: Mathematics & Statistics, Univ. of Mass./Amherst
- References: <f86r55$pc7$1@smc.vnet.net> <200707250930.FAA26363@smc.vnet.net> <f89pve$5jn$1@smc.vnet.net> <200707261030.GAA09683@smc.vnet.net>
- Reply-to: murray at math.umass.edu
Very nice! An observation and a question:
1. Probably it would be more reasonable that the third, optional,
argument be not an {x,y} point, but instead the x-coordinate of that
point, since the point is supposed to be on the graph anyway. The
modification for that is trivial:
trackPointOnPlot[f_, {a_, b_}, strt_: Automatic] :=
Module[{start = strt /. Automatic -> a},
DynamicModule[{p = {start, f[start]}},
Column[{LocatorPane[Dynamic[p, (p = {First@#, f[First@#]}) &],
Plot[f[x], {x, a, b}]], Dynamic[p]}]]]
2. Where/how did you discover the "trick" of using Automatic as a
default value for an argument? I don't recall seeing that before.
Albert wrote:
> ...The following is my attempt to solve your issue, it only uses one
> definition, but introduces some extra code...
>
> trackPointOnPlot[f_, {a_, b_}, strt_: Automatic] :=
> Module[{start = strt /. Automatic -> {a, f[a]}},
> DynamicModule[{p = start},
> Column[{LocatorPane[Dynamic[p, (p = {First@#, f[First@#]}) &],
> Plot[f[x], {x, a, b}]], Dynamic[p]}]]
> ]
Of course, per your suggestion, a simpler way but now using only the
x-coordinate as third, optional, argument is:
trackPointOnPlot[f_, {a_, b_}, start_] :=
DynamicModule[{p = {start, f[start]}},
Column[{LocatorPane[Dynamic[p, (p = {First@#, f[First@#]}) &],
Plot[f[x], {x, a, b}]], Dynamic[p]}]]
trackPointOnPlot[f_, {a_, b_}] := trackPointOnPlot[f, {a, b}, a]
--
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: Albert <awnl@arcor.net>
- Re: Locator question
- From: Albert <awnl@arcor.net>
- Re: Locator question