Texas Instruments PLUS TI-89 - Manual (Page 185)

168 Chapter 10: 3D Graphing
10_3D.DOC TI-89/TI-92 Plus: 3D Graphing (English) Susan Gullord Revised: 02/23/01 11:00 AM Printed: 02/23/01 4:22 PM Page 168 of 22 10_3D.DOC TI-89/TI-92 Plus: 3D Graphing (English) Susan Gullord Revised: 02/23/01 11:00 AM Printed: 02/23/01 4:22 PM Page 168 of 22
You can set the ncontour Window variable ( ¥ $ ) to specify the
number of contours that will be evenly distributed along the
displayed range of z values, where:
increment =
zmax ì zmin
ncontour + 1
The z values for the contours are:
zmin + increment
zmin + 2(increment)
zmin + 3(increment)
©
zmin + ncontour(increment)
If ncontour=5 and you use the standard viewing window ( zmin= ë 10
and zmax=10 ) , the increment is 3.333. Five contours are drawn for
z=л 6.666, л 3.333, 0, 3.333, and 6.666.
Note, however, that a contour is not drawn for a z value if the 3D
graph is not defined at that z value.
If a contour graph is currently displayed, you can specify a point on
the graph and draw a contour for the corresponding z value.
1. To display the Draw menu, press:
TI
-
89: 2 ˆ
TI
-
92 Plus : ˆ
2. Select 7:Draw Contour .
3. Either:
¦ Type the point’s x value and press
¸, and then type the y value
and press ¸.
– or –
¦ Move the cursor to the applicable point. (The cursor moves
along the grid lines.) Then press ¸.
For example, suppose the current graph is z1(x,y)=x ñ +.5y с м 5 . If you
specify x=2 and y=3, a contour is drawn for z=3.5.
How Are Z Values
Determined?
Drawing a Contour
for the Z Value of a
Selected Point
Interactively
Tip: Any existing contours
remain on the graph. To
remove the default contours,
display the Window editor
(
¥ $ ) and set
ncontour=0 .
The default is 5. You can
set this to 0 through 20.