How to Graph Sequences & Phase Plots on TI-Nspire

By Jeff McCalla, Steve Ouellette

When graphing on the TI-Nspire, the initial condition (or term) is always graphed with a green point which can be grabbed and moved to investigate the behavior in terms of the initial condition or term.

To demonstrate the dynamic nature of sequence graphs, in this example enter two sequences that represent the population of rabbits and foxes. Of course, the population of predators is related to the population of its prey.

Press [MENU]→Graph Type→Sequence→Sequence to enter the sequence for rabbits: u1=u1(n–1)·(1.05–.001·u2(–1), initial condition=200, 0<n<500. See the first screen. In the sequence for foxes, u2 = u2(n–1)·(0.97+.0002·u1(n–1), initial condition=50, 0<n<500. See the graph of both sequences in the second screen.


If you want to see how one sequence affects another sequence, you can use a phase plot to represent the data. Here are the steps to create a phase plot:

  1. Press [CTRL][I]→Add Graphs.

  2. Press [MENU]→Graph Type→Sequence→Custom.

  3. Enter u1 for x and u2 for y with 1<n<300.

  4. Press [ENTER] to graph the phase plot.

  5. Adjust your window by pressing [MENU]→Window/Zoom→Zoom Fit.

You can grab and move the point that represents the initial condition right on the graph screen.