I/O and Hardcopy

XPP has many options that allow you to save the state of the system, data generated by the program, postscript figures, etc. We have not looked at these in the tutorial in order to avoid clogging up temporary directories formed by the Web Browser with files that you won't need for the tutorials. However, for the homeworks, it is best to make hard copy so that they can be looked at by the instructors.

This section presents a howto for different types of input and output that you will want for general use of the program.

Saving and loading numerical data

XPP lets you save data from the calculations you have done either in XPP or in AUTO. Any data in the Data Browser can be written to a file. In the Data Browser window, just click on (Write) and give the filename. The data is saved in ASCII format with each row in the file corresponding to a row in the Browser. The separator between numbers is a space.

Similarly, any file that has this simple format can be read by XPP and plotted within the program. XPP will only load in as many columns as it has allocated.

Within the AUTO window , you can write the numerical values that appear on the bifurcation diagram in a three column file containing the parameter in the first column, the minimum in the second and the maximum in the third column. To do this, within the AUTO window, click (File) (Write Pts) and give a filename.

Saving and loading states

XPP allows you to save some aspects of the program that you can later reload and thus keep track of initial data, parameters, window dimensions, and numerical parameters. By convention, these are called .set files. From the main XPP menu, click on (File) and then (Write set) to save the state of XPP. You will be asked for a filename.

Similarly, click on (File) (Read set) to get the saved state.

XPP lets you write a "Human Readable" version of this by clicking (File) (Save info) to write to a file and (File) (Prt info) to write to the terminal.

Saving and loading bifurcation diagrams

If you compute a bifurcation diagram, you can save it. Saving a diagram also saves all the numerical and plotting parameters as well. ( Note. I often save AUTO diagrams after setting up all the AUTO parameters but before computing anything as all this information is then conveniently saved for later use.) You can also load previously saved diagrams. Within AUTO click on (File) (Save diagram) and give a filename to save the diagram. To reuse it after saving it, click on (File) (Load diagram).

Printing and hardcopy

XPP can create PostScript files of the graphs that are on the screen. These can then be used in documents such as TeX since they provide the Bounding Box information required. To print out XPP graphics, from the main XPP window, click on (Graphics) (Postscript) and provide a filename.

To make a postscript file for a bifurcation diagram, within the AUTO window, click (File) (Postscript) and enter a filename.

Form of OPTIONS files

You can have many options files. They are useful for initializing XPP. They have the following format: 
9x15    BIG_FONT_NAME   <-- menu fonts
fixed   SMALL_FONT_NAME <-- IC, browser, etc fonts
0       BACKGROUND (1=white,0=black)
0	IXPLT <--  X-axis variable (0=time)
1	IYPLT <--  Y-axis variable
1	IZPLT <--  Z-axis variable
3	AXES <-- type of axis
1	NJMP <-- nOutput
40	NMESH <-- Nullcline mesh
4	METHOD <-- Integration method
1	TIMEPLOT <--- set to zero if one axis is not time
8000	MAXSTOR <--- maximum rows stored
20.0	TEND <-- total integration time
.05	DT <--- time step
0.0	T0 <-- start time
0.0	TRANS <-- transient
100.	BOUND <--- bounds
.0001	HMIN <-- min step for GEAR
1.0	HMAX <-- max ``   ``   ``
.00001	TOLER <-- tolerance for GEAR
0.0	DELAY <-- maximal delay
0.0	XLO  <--- 2D window sizes
20.0	XHI
-2.0	YLO
2.0	YHI

References