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 2210_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 ( ¥$) to specify the
number of contours that will be evenly distributed along the
displayed range of z values, where:
increment =
zmax ìzmin
ncontour + 1
The z values for the contours are:
zmin + increment
zmin + 2(increment)
zmin + 3(increment)
©
zmin + ncontour(increment)
If ncontour=5 and you use the standard viewing window (zmin=ë10
and zmax=10) , the increment is 3.333. Five contours are drawn for
z=ë6.666, ë3.333, 0, 3.333, and 6.666.
Note, however, that a contour is not drawn for a z value if the 3D
graph is not defined at that z value.
If a contour graph is currently displayed, you can specify a point on
the graph and draw a contour for the corresponding z value.
1. To display the Draw menu, press:
TI-89: 2ˆ
TI-92 Plus: ˆ
2. Select 7:Draw Contour.
3. Either:
¦ Type the point’s x value and press
¸, and then type the y value
and press ¸.
– or –
¦ Move the cursor to the applicable point. (The cursor moves
along the grid lines.) Then press ¸.
For example, suppose the current graph is z1(x,y)=xñ+.5yñì5. If you
specify x=2 and y=3, a contour is drawn for z=3.5.
How Are Z Values
Determined?
Drawing a Contour
for the Z Value of a
Selected Point
Interactively
Tip: Any existing contours
remain on the graph. To
remove the default contours,
display the Window editor
(
¥$)
and set
ncontour=0
.
The default is 5. You can
set this to 0 through 20.