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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"><HTML>
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<TITLE> Description of Objects in VPython</TITLE>
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<b class="navlabel">Previous:</b> <a class="sectref" HREF="vector.html">The vector Object</A>
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<b class="navlabel">Next:</b> <a class="sectref" HREF="display.html">Controlling Windows</A>
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</DIV>
<DIV>
<H1 CLASS="Heading-1"> <font color="#0000A0">Graph Plotting</font></H1>
</DIV>
<DIV>
<P CLASS="Normal"> In this section we describe features for plotting graphs
with tick marks and labels. Here is a simple example of how to plot a graph:</P>
</DIV>
<DIV>
<DIV>
<H2 CLASS="program0">
from visual.graph import * # import graphing features</H2>
</DIV>
<DIV>
<H2 CLASS="program0">
</H2>
</DIV>
<DIV>
<H2 CLASS="program0">
funct1 = gcurve(color=color.cyan) # a connected curve object</H2>
</DIV>
<DIV>
<H2 CLASS="program0">
</H2>
</DIV>
<DIV>
<H2 CLASS="program0">
for x in arange(0., 8.1, 0.1): # x goes from 0 to 8</H2>
<P CLASS="program">
funct1.plot(pos=(x,5.*cos(2.*x)*exp(-0.2*x))) # plot</P>
<P CLASS="Normal"> Importing from <span class="attribute">visual.graph</span>
makes available all Visual objects plus the graph plotting module. The graph
is autoscaled to display all the data in the window.</P>
<P CLASS="Normal"> A connected curve (<span class="attribute">gcurve</span>)
is just one of several kinds of graph plotting objects. Other options are
disconnected dots (<span class="attribute"><span class="attribute">gdot</span>s</span>),
vertical bars (<span class="attribute">gvbars</span>), horizontal bars (<span class="attribute"><span class="attribute">ghbar</span>s</span>),
and binned data displayed as vertical bars (<span class="attribute">ghistogram</span>;
see later discussion). When creating one of these objects, you can specify
a color attribute. For <span class="attribute">gvbars</span> and <span class="attribute">ghbars</span>
you can also specify a <span class="attribute">delta</span> attribute, which
specifies the width of the bar (the default is <span class="attribute">delta=1.</span>).</P>
<P CLASS="Normal">
You can plot more than one thing on the same graph:</P>
</DIV>
<DIV>
<H2 CLASS="program0">
funct1 = gcurve(color=color.cyan) </H2>
<P CLASS="program"> funct2 = gvbars(delta=0.05, color=color.blue)</P>
</DIV>
<DIV>
<H2 CLASS="program0">
for x in arange(0., 8.1, 0.1): </H2>
</DIV>
<H2 CLASS="program0">
funct1.plot(pos=(x,5.*cos(2.*x)*exp(-0.2*x))) # curve</H2>
<P CLASS="program">
funct2.plot(pos=(x,4.*cos(0.5*x)*exp(-0.1*x))) # vbars</P>
<P CLASS="Normal">
In a plot operation you can specify a different color to override the original setting:</P>
<DIV>
<H2 CLASS="program0">
mydots.plot(pos=(x1,y1), color=color.green) </H2>
<P CLASS="Normal"> When you create a <span class="attribute">gcurve</span>,
<span class="attribute">gdots</span>, <span class="attribute"><span class="attribute">gvbar</span>s</span>,
or <span class="attribute">ghbars</span> object, you can provide a list
of points to be plotted, just as is the case with the ordinary <span class="attribute">curve</span>
object:</P>
</DIV>
<DIV>
<H2 CLASS="program0">
points = [(1,2), (3,4), (-5,2), (-5,-3)]</H2>
<P CLASS="program"> data = gdots(pos=points, color=color.blue)</P>
<P CLASS="Normal">This list option is available only when creating the <span class="attribute">gdots</span>
object.</P>
<P CLASS="Normal"> </P>
<P CLASS="Normal"><font color="#0000A0">Overall gdisplay options</font></P>
<P CLASS="Normal">You can establish a <span class="attribute">gdisplay</span>
to set the size, position, and title for the title bar of the graph window,
specify titles for the x and y axes, and specify maximum values for each
axis, before creating <span class="attribute">gcurve</span> or other kind
of graph plotting object:</P>
</DIV>
</DIV>
<DIV><DIV>
<H2 CLASS="program0">
graph1 = gdisplay(x=0, y=0, width=600, height=150, </H2>
<P CLASS="program"> title='N
vs. t', xtitle='t', ytitle='N', </P>
<P CLASS="program"> xmax=50.,
xmin=-20., ymax=5E3, ymin=-2E3, </P>
<p class="program"> foreground=color.black,
background=color.white)</p>
<P CLASS="Normal"> In this example, the graph window will be located at (0,0),
with a size of 600 by 150 pixels, and the title bar will say 'N vs. t'.
The graph will have a title 't' on the horizontal axis and 'N' on the vertical
axis. Instead of autoscaling the graph to display all the data, the graph
will have fixed limits. The horizontal axis will extend from -20. to +50.,
and the vertical axis will extend from -2000. to +5000. (xmin and ymin must
be negative; xmax and ymax must be positive.) The foreground color (white
by default) is black, and the background color (black by default) is white.
If you simply say <span class="attribute">gdisplay()</span>, the defaults
are <span class="attribute">x=0</span>, <span class="attribute">y=0</span>,
<span class="attribute">width=800</span>, <span class="attribute">height=400</span>,
no titles, fully autoscaled.</P>
<P CLASS="Normal"> Every gdisplay has the attribute <span class="attribute">display</span>,
so you can manipulate basic display aspects of the graphing window:</P>
<h2 class="program0">graph1.display.visible = 0 # make the display invisible
</h2>
<p class="program"> </p>
<P CLASS="Normal">You can have more than one graph window: just create another
<span class="attribute"> gdisplay</span>. By default, any graphing objects
created following a <span class="attribute">gdisplay</span> belong to that
window. You can also specify which window a new object belongs to: </P>
</DIV>
<DIV>
<H2 CLASS="program0"> energy = gdots(gdisplay=graph1, color=color.blue)</H2>
<p class="Normal"> </p>
<p class="Normal"><font color="#0000A0">Histograms (sorted, binned data)</font></p>
<h2 class="attribute"></h2>
</DIV>
</DIV>
<DIV>
<P CLASS="Normal">The purpose of <span class="attribute">ghistogram</span> is
to sort data into bins and display the distribution. Suppose you have a list
of the ages of a group of people, such as [5, 37, 12, 21, 8, 63, 52, 75, 7].
You want to sort these data into bins 20 years wide and display the numbers
in each bin in the form of vertical bars. The first bin (0 to 20) contains
4 people [5, 12, 8, 7], the second bin (20 to 40) contains 2 people [21, 37],
the third bin (40 to 60) contains 1 person [52], and the fourth bin (60-80)
contains 2 people [63, 75]. Here is how you could make this display:</P>
<DIV>
<H2 CLASS="program0">
from visual.graph import * </H2>
<P CLASS="program">
.....</P>
</DIV>
<DIV>
<H2 CLASS="program0"> agelist1<EM CLASS="code"> = </EM>[5, 37, 12, 21, 8, 63,
52, 75, 7] </H2>
</DIV>
<DIV>
<H2 CLASS="program0">
ages = ghistogram(bins=arange(0, 80, 20), color=color.red) </H2>
</DIV>
<DIV>
<H2 CLASS="program0">
ages.plot(data=agelist1) # plot the age distribution</H2>
</DIV>
<DIV>
<H2 CLASS="program0">
.....</H2>
</DIV>
<DIV>
<H2 CLASS="program0">
ages.plot(data=agelist2) # plot a different distribution</H2>
<P CLASS="Normal"> You specify a list (bins) into which data will be sorted.
In the example given here, bins goes from 0 to 80 by 20's. By default, if
you later say</P>
</DIV>
<DIV>
<H2 CLASS="program0">
ages.plot(data=agelist2)</H2>
<P CLASS="Normal">
the new distribution replaces the old one. If on the other hand you say</P>
</DIV>
<DIV>
<H2 CLASS="program0">
ages.plot(data=agelist2, accumulate=1)</H2>
<P CLASS="Normal">
the new data are added to the old data. </P>
<P CLASS="Normal">
If you say the following, </P>
</DIV>
<DIV>
<H2 CLASS="program0">
ghistogram(bins=arange(0,50,0.1), accumulate=1, average=1)</H2>
<P CLASS="Normal"> each plot operation will accumulate the data and average the
accumulated data. The default is no accumulation and no averaging.</P>
<P CLASS="Normal"> </P>
</DIV>
</DIV>
<DIV>
<div>
<div>
<p class="Normal"><font color="#0000A0">gdisplay vs. display</font></p>
<h2 class="attribute"></h2>
</div>
</div>
<div> A gdisplay window is closely related to a display window. The main difference
is that a gdisplay is essentially two-dimensional and has nonuniform x and
y scale factors. When you create a gdisplay (either explicitly, or implicitly
with the first gcurve or other graphing object), the current display is saved
and restored, so that later creation of ordinary Visual objects such as sphere
or box will correctly be associated with a previous display, not the more
recent gdisplay.</div>
<P CLASS="Normal"> </P>
</DIV>
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