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Appendix A: Functions and Instructions 521
8992APPA.DOC TI-89 / TI-92 Plus: Appendix A (US English) Susan Gullord Revised: 02/23/01 1:48 PM Printed: 02/23/01 2:21 PM Page 521 of 132
For polynomial systems, computation time or
memory exhaustion may depend strongly on
the order in which you list unknowns. If your
initial choice exhausts memory or your
patience, try rearranging the variables in the
expressions and/or
varOrGuess
list.
If you do not include any guesses and if any
expression is non-polynomial in any variable
but all expressions are linear in the
unknowns,
zeros()
uses Gaussian elimination
to attempt to determine all real zeros.
zeros({x+
e
^(z)
ù
y
ì
1,x
ì
y
ì
sin(z)}
,{x,y})
¸
e
z
ø
sin(z)+1
e
z
+1
ë
(sin(z)
ì
1)
e
z
+1
If a system is neither polynomial in all of its
variables nor linear in its unknowns,
zeros()
determines at most one zero using an
approximate iterative method. To do so, the
number of unknowns must equal the number
of expressions, and all other variables in the
expressions must simplify to numbers.
Each unknown starts at its guessed value if
there is one; otherwise, it starts at 0.0.
zeros({
e
^(z)
ù
y
ì
1,
ë
y
ì
sin(z)},
{y,z})
¸
[]
.041… 3.183…
Use guesses to seek additional zeros one by
one. For convergence, a guess may have to
be rather close to a zero.
zeros({
e
^(z)
ù
y
ì
1,
ë
y
ì
sin(z)},
{y,z=2p})
¸
[]
.001… 6.281…
ZoomBox
CATALOG
ZoomBox
Displays the Graph screen, lets you draw a
box that defines a new viewing window, and
updates the window.
In function graphing mode:
1.25x
ù
cos(x)
!
y1(x)
¸
Done
ZoomSt
d
:ZoomBox
¸
The display after defining
ZoomBox
by
pressing
¸
the second time.
1st corner
2nd corner