The Geometer’s Sketchpad
®
for TI-89, TI-92 Plus, and
© 2000-2002 KCP Technologies, Inc.
87
Voyage™ 200 PLT User Guide and Reference Manual
evaluated in order to determine the overall shape of the plot. A higher
number of samples leads to smoother images, but a lower number of
samples leads to faster dragging.
Become familiar with how and when to change the number of samples in a
plotted locus or construction—see Locus Properties (page 47), Graph
Properties (page 48), and Plot Preferences (page 52). You might wish to
keep your Preferences settings to a very low number of samples for new
loci and function plots. Then, once you’ve created a locus or function plot,
if its display accuracy is not adequate, increase the number of samples for
that plot only, using its Properties dialog box.
After you’ve manipulated and dragged your construction, if you’re
interested in a very smooth final image, position the plot as you’d like to
see it and then set its Properties to a very high number of samples. If your
locus or function is sufficiently complex, and you’ve requested 800
samples, Sketchpad may take several minutes to evaluate a single image of
it. Don’t try to drag the plot when its number of samples is so high!
Instead, consider using animation in conjunction with tracing to generate a
series of (traced) images at high resolution.
While grids are not challenging objects mathematically, they can be slow
to display and to drag because the slightest change to a grid requires the
entire screen to be redrawn. Unless a coordinate system investigation
specifically requires a visible grid, consider hiding the grid before dragging
objects. On the small screen of a graphing calculator, hiding the grid may
also improve the legibility of your sketch.
Keep in mind that Sketchpad supports unlimited undo and redo of basic
operations (see page 42). Though very powerful, unlimited undo has a
cost—it uses program memory to remember every basic action you’ve
performed in your sketch. Thus whenever you delete objects in a sketch
(see Delete, page 43), Sketchpad deletes them from the screen, but cannot
delete them from memory because you might wish to undo the deletion
later. Over time, deleted objects take up memory on your graphing
calculator that could better be put to other uses. While you should feel free
to delete objects whenever you need to, it pays to keep in mind some tips
for using the Delete command wisely:
1. If you wish to remove an object you’ve just created, Undo that object
rather than Delete it. If you undo it, Sketchpad can release the
memory it uses to remember where that object was created.
2. If you wish to start work in a blank sketch, use
ƒ
Edit:
o
Sketch:
¨
New rather than selecting all and then choosing
ƒ
Edit:
ª
Delete [Objects]. Moving to a new sketch lets Sketchpad release all
the memory it uses to remember objects in your previous sketch.
3. If Sketchpad ever warns you that you are running low on memory,
refresh your undo history by saving (see Unlimited Undo and
Memory, page 42, for instructions on how to do this). Then delete any
unneeded sketches from the VAR-LINK page. To do this, press
2
°
to access the VAR-LINK main menu. Use the cursor
pad to scroll down to any unneeded file (Sketchpad files are listed as
GSP). With the unneeded file selected, press
†
to put a check by its
name. In the same way, put checks by the names of all unneeded
files. Now press
ƒ
Manage:
¨
Delete to delete the file(s). Press
¸
to confirm the deletion. When you’re done deleting files, press
N
to return to Sketchpad.
Grids
Delete vs. Undo
