General features

Launching the Iode graphical user interface (see instructions in Appendix B) gets you to the main menu:

Direction fields

Phase planes

Second order linear ODEs

Fourier series

Partial differential equations

Exit

You can launch these modules independently, and can even launch multiple copies of each module. Before looking at these modules in detail, we explain some features that are common to all (or most) of them.

Every window contains one or two graphs, as well as a number of controls for affecting those graphs. And across the top of each window is a menu bar whose entries include File, Equation (or Function), and Options.

The File menu deals with the outside world, such as files and printers. The Equation menu deals with the mathematical content of your window, i.e., it controls what you're looking at. The Options menu contains the display options, i.e., it controls how you're looking at the contents of your window.

Next we describe those menu items that are shared by all modules. Then we'll come to more detailed chapters on each module in turn.

File menu

The File menu is the same for all components of Iode.

• Open a file containing previously-saved settings for the window.
• Save a file containing the current settings of the window. (The file name should be entered in the Selection window of the dialog box, and should have extension .mat.) The point is that you can Save your work and then Open it again later.
• Print. By default, this will print the entire current window. If you just want to print the graphs and not the rest of the window, choose Print and then click on the Options button. In the resulting dialog, check the box labeled ``Suppress printing of user interface controls'', then click on OK.

  If you choose to print to a file instead of to a printer then you can write your plot as a .ps file, which can then be opened and viewed with Ghostview. (For example, on a Unix system you would get to a Unix prompt, outside of Matlab, and type ghostview my_plot.eps.)

• Quit will exit from the module.

Equation (or Function) menu

The Equation (or Function) menus have just one entry in common.

• Relabel variables: this item allows you to choose new names for the independent as well as dependent variables.

Options menu

The Options menus have one entry in common.

• Enter caption: this item lets you put a caption at the very bottom of the window, and is useful for adding annotations (e.g., your name, or the number of a homework assignment).

Miscellaneous features

[Error handling.] In any of Iode's dialog boxes, if Iode cannot make sense of the information you provide then it will produce an error message and simply keep the previous values. For example, a common mistake is to forget to type ``*'' to indicate multiplication. If you are asked to enter a function and type $2xy$ as 2xy, then Iode will report an error and will continue using the previous function. (The correct input for $2xy$ is 2*x*y.)

[Interrupting.] Matlab lacks proper mechanisms for interrupting lengthy computations, so that there are only two solutions if a computation takes a long time to finish: Either you wait until the computation is done, or you quit from Matlab altogether. The good news is that you won't encounter lengthy computations unless you explicitly request them, e.g., by choosing an inordinately small step size for numerical computations.