Texas Instruments TITANIUM TI-89 - Manual (Page 449)

Differential Equation Graphing 449
Fields=SLPFLD Fields=SLPFLD Fields=SLPFLD Fields=SLPFLD
In the
Y= Editor Use
†
to select one and only one 1st-order equation. You
can enter mulNotele equations, but only one at a time can be
selected.
The selected equation must not refer to any other equation in
the Y= Editor. For example:
If y1'=y2, an Undefined variable error occurs when you graph.
In the Graph
screen If the slope field is drawn but no solution curve is plotted,
specify an initial condition.