Re: Q> on COMBINING PLOTS w/ diff. axes. (LONG)

• Subject: [mg2659] Re: [mg2607] Q> on COMBINING PLOTS w/ diff. axes. (LONG)
• From: nichols at godel.math.cmu.edu (Preston Nichols)
• Date: Sun, 3 Dec 1995 02:53:42 -0500
• Approved: usenet@wri.com
• Distribution: local
• Newsgroups: wri.mathgroup
• Organization: Wolfram Research, Inc.

```Zorro <berriz at husc.harvard.edu> asked:

"So my question are 1) in general, how does one get Mathematica to
superimpose plots with different units on the vertical or horizontal
axis, and 2) in particular, how does one get it to display histograms
and functions together?"
--------------------------------------------------------------------
Both issues are addressed by the functionality of the FullGraphics
command.

In[1]:=
?FullGraphics
FullGraphics[g] takes a graphics object, and generates a
new one in which objects specified by graphics options
are given as explicit lists of graphics primitives.

The "objects specified by graphics options" are principally axes
and ticks, and FullGraphics "protects" them from Mathematica's
default procedures for graphics options.

Here are some examples which illustrate the use of FullGraphics
when combining 2D graphics.  (The  later ones  use the results of
the earlier ones, so if you try them out, be sure to execute them in
order.  I made this message as a Notebook, available at
http://www.contrib.andrew.cmu.edu/usr/pdn/CombinePlot.ma.)  Plot1
will serve as a "fixed" reference plot,and will not be transformed;
Plot2 will be altered and overlayed on Plot1 in various ways.

First, without FullGraphics:

In[2]:=
Plot1 = Plot[Sin[x], {x,0,2 Pi}];
Plot2 = Plot[Sin[x], {x,0,Pi},AxesOrigin->{Pi,1}];
Show[{Plot1,Plot2}];

The same plots, using FullGraphics:

In[5]:=
FullPlot1 = Plot1//FullGraphics;
FullPlot2 = Plot2//FullGraphics;
Show[{FullPlot1,FullPlot2}];

Be sure to note the effect of the AxesOrigin option in Plot2.
--------------------------------------------------------------------
If we want the two plots, when displayed simutaneously, to occupy
the same horizontal space on the screen (or page) even though their
abscissas have different ranges, we can use:

In[8]:=
Needs["Graphics`Graphics`"];
?SkewGraphics
SkewGraphics[graphics, m] applies the matrix m to all
coordinates in graphics.

So (just to have an example) let's stretch Plot2 horizontally by a
factor of 2, by using SkewGraphics on the FullGraphics version of
Plot2:

In[10]:=
SkewFullPlot2 = SkewGraphics[FullPlot2, {{2,0},{0,1}}];
Show[SkewFullPlot2];
Show[{FullPlot1,SkewFullPlot2}];

Note how the two distinct abscissa scales appear.  And again take
note of the effect of the AxesOrigin option.
--------------------------------------------------------------------
For this to work properly, the use of FullGraphics is essential,
and it is important that FullGraphics is applied before
SkewGraphics.  If the opposite order is used, the "data" in the plot
will be Skew'ed, but not the coordinate scale(s):

In[13]:=
FullSkewPlot2 = SkewGraphics[Plot2, {{2,0},{0,1}}]//FullGraphics;
Show[FullSkewPlot2];
Show[{FullPlot1,FullSkewPlot2}];
--------------------------------------------------------------------
The ordinate scales can be manipulated in the same way as the
abscissa scales have been, just by using a suitable matrix in
SkewGraphics.  If the scales to be superimposed are related by
nonlinear functions, TranformGraphics can be used in place of
SkewGraphics.

In[16]:=
?TransformGraphics
TransformGraphics[graphics, f] applies the function f to
all lists of coordinates in graphics.

Here's a toy example.

In[17]:=
f[{x_,y_}] := {2 x Exp[x]/Exp[Pi],y^2}

In[18]:=
TransformFullPlot2 = TransformGraphics[FullPlot2, f];
Show[TransformFullPlot2];
Show[{FullPlot1,TransformFullPlot2}];

As this example suggests, in many cases it may work better to
generate the original Plots with one of the versions of ScaledPlot
or  LogPlot, and then Skew the results linearly.
--------------------------------------------------------------------
Here's an example with a BarChart version of Plot2.

In[21]:=
BarPlot2 = BarChart[Table[Sin[x], {x,0,Pi,Pi/6}],
AxesOrigin->{7,1}];

In[22]:=
FullBarPlot2 = BarPlot2//FullGraphics;
SkewFullBarPlot2 =
SkewGraphics[FullBarPlot2, {{Pi/3,0},{0,1}}];
Show[{FullPlot1,SkewFullBarPlot2}];

Since that's not quite "right", try this affine transformation:

In[24]:=
TransformFullBarPlot3 =TransformGraphics[
FullBarPlot2, ({{Pi/3,0},{0,1}}.(# -{1,0}))&];
Show[{FullPlot1,TransformFullBarPlot3}];
--------------------------------------------------------------------
Preston Nichols
Visiting Assistant Professor
Department of Mathematics
Carnegie Mellon University

```

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