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MathGroup Archive 2007

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Dynamic 2D Plotting in V6

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76157] Dynamic 2D Plotting in V6
  • From: Todd Allen <genesplicer28 at yahoo.com>
  • Date: Thu, 17 May 2007 05:52:00 -0400 (EDT)

Hello All,

   First, let me congratulate WRI on the release of
Version 6....I think many of us are finding "golden
nuggets" that make this a very fun release to have in
our hands.

   I'm an educator and have always been interested in
finding a way to explain the concept of pH (defined as
the free concentration of hydrogen ions in a solution)
to my biology students.  Plotting pH graphically has
always been out of the question because of the
tremendous range of values that pH relies upon (from
1*10^-14 to 1).  When I saw that Version 6 has dynamic
updating ability, I became excited with the
possibility that V6 might dynamically update one or
both axes on a graph and finally make it possible to
show students how pH changes as you vary the hydrogen
ion concentration.

   If you have V6, please copy-paste the following
short code and you can see how the slider bar does
change the x-axis (in this case the hydrogen ion
concentration) dynamically.

Code:

test2 = {Slider[Dynamic[h]], 
  Dynamic[Plot[-Log[10, h], {h, 1/10^14, 1}, 
    PlotRange -> {{0, h}, {0, 14}}]]}


The problem is that most of the interesting change in
the pH value is "compressed" along the leftmost side
of the slider so that the smooth, gradual increase in
pH (as hydrogen levels drop) is not well illustrated. 
The graph itself looks "tied" to a pH value of 8, when
at very low hydrogen concentrations there should be a
nice gradual curve towards a pH of 14.

Would anyone have any ideas how to solve this
compression issue and make the graph more illustrative
to students?

Happy computing!
Todd



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