Here are some instructions for starting on your 0th computer assignment. The professor who constructed and kept up up the netmath pages, Bill Schelter, died of at a heart attack last year. We will sorely miss him but for your first assignment, give his program, netmath, a try.

1) Log in, with the help of the address and login number assigned to you. You may change the password, but don't forget either the password or your login number.

2) Type netmath. Arrange the little window which appears in the upper corner. Click. If the big window which appears covers your other windows, you can find them again by putting the curser in the vacant part of your screen and pressing the right button. All your active windows are listed here.

3) Go down and click on course material for differential equations. Click on direction field stuff. Play around with clicking on the blue typing, and look for some solutions of the differential equations.   [When you get a plot, you can adjust the parameters or dismiss the plot by bringing your mouse to the upper left hand corner and waiting for a menu to drop down]

Your zeroth assignment is to graph solutions of the equation
y' = .5y - .1 y^2
through the point y = .2 at t = 0 and then through the point y = 7 at t= 0.
We are interested in the motion that is forward, and I am asking you to give it to me between t= 0 and t= 10. If you use the settings that are given, even after you have typed (correctly) d(y,x) = .5* - .1*y*y* in place of the first equation, your graph will not be beautiful.  To get a decent looking graph you set to set the scale and center correctly.  I got a very nice graph by going to the upper left corner and changing the config to
n steps 1000
t initial 0
y center 5
x center 6
y radius 6
x radius 7
and then clicking on okay and hitting replot in the same menu I got config from. See if you can get the motion to go forward only. Change color and width of the function graph. Click on dismiss to start again. Do not click on back (this takes you back to a previous netmath page). If you really mess things up, log out of netmath and then back in again. All your mess will be gone!

As a second exercise, try graphing a bunch of solutions to

y' = .1 y(y-1)(y-2)

The really interesting stuff happens between about y = -1 and y = 3. So make some adjustments and produce some graphs of this. You might read the rest of this page as well.

If you're looking for more to do, computer assignment one will be posted on the web shortly. It's likely to closely resemble computer assignment 1 from last year, which can be found at  www.ma.utexas.edu/users/uhlen/bio/computer1.