Texas Instruments TITANIUM TI-89 - Manual (Page 422)

Differential Equation Graphing 422
If You Do Not Enter an Initial Condition in the Y= Editor If You Do Not Enter an Initial Condition in the Y= Editor If You Do Not Enter an Initial Condition in the Y= Editor If You Do Not Enter an Initial Condition in the Y= Editor
If you do not enter initial conditions, the ncurves Window variable ( 8 $) specifies
the number of solution curves graphed automatically. By default, ncurves = 0 . You can
enter a value from 0 through 10. However, the Fields graph format and the Axes setting
determine whether ncurves is used.
When ncurves is used, t0 is set temporarily at the middle of the Graph screen. However,
the value of t0 as set in the Y= Editor or Window Editor is not changed.
Notes:
• Without entering initial conditions, use SLPFLD (with ncurves=0 ) or DIRFLD to
display a slope or direction field only.
• SLPFLD is for a single 1st-order equation only. DIRFLD is for a 2nd-order equation
(or system of two 1st-order equations) only.
If Fields = Then:
SLPFLD Uses ncurves, if not set to 0, to graph curves.
DIRFLD Ignores ncurves. Does not graph any curves.
FLDOFF Uses ncurves if Axes = TIME (or if Axes = Custom and the
x axis is t). Otherwise, a Diff Eq setup error occurs.