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Truth plots
Truth plots are used to produce two-dimensional plots of regions that satisfy a
certain mathematical condition that can be either true or false. For example,
suppose that you want to plot the region for X^2/36 + Y^2/9 < 1,
proceed as follows:
Θ Press „ô, simultaneously if in RPN mode, to access to the PLOT SETUP
window.
Θ Change
TYPE to Truth.
Θ Press ˜ and type {‘(X^2/36+Y^2/9 < 1)','(X^2/16+Y^2/9 > 1)’}
@@@OK@@@ to define the conditions to be plotted.
Θ The cursor is now in the
Indep field. Leave that as ‘X’ if already set to that
variable, or change it to ‘X’ if needed.
Θ Press L@@@OK@@@ to return to normal calculator display.
Θ Press „ò, simultaneously if in RPN mode, to access the PLOT window
(in this case it will be called PLOT WINDOW – TRUTH window). Let’s keep
the default value for the window’s ranges:
H-View: -6.5 6.5, V-View:
-3.9 4.0 (To
reset them use L @RESET (select Reset all) @@OK@@ L).
Θ Press @ERASE @DRAW to draw the truth plot. Because the calculator samples the
entire plotting domain, point by point, it takes a few minutes to produce a
truth plot. The present plot should produce a shaded ellipse of semi-axes 6
and 3 (in x and y, respectively), centered at the origin.
Θ Press @EDIT L @LABEL @MENU to see the graph with labels. The window
parameters are such that you only see half of the labels in the x-axis. Press
L to recover the menu. Press L@)PICT to recover the original graphics
menu.
Θ Press (X,Y) to determine coordinates of any point on the graph. Use the
arrow keys to move the cursor about the region plotted. At the bottom of
the screen you will see the value of the coordinates of the cursor as (X,Y).
Θ Press L@)CANCL to return to the PLOT WINDOW environment. Then, press
$ , or L@@@OK@@@, to return to normal calculator display.
You can have more than one condition plotted at the same time if you multiply
the conditions. For example, to plot the graph of the points for which X
2
/36 +
Y
2
/9 < 1, and X
2
/16 + Y
2
/9 > 1, use the following:
Note: if the window’s ranges are not set to default values, the quickest way to
reset them is by using L@RESET@ (select Reset all) @@@OK@@@ L.