HOW TO USE NETMATH TO DO YOUR FIRST COMPUTER ASSIGNMENT I recommend that two people work together. It minimizes the really stupid errors. Hopefully you have tried NETMATH, but if not, let me remind you to log in. The lab proctors can help you with this sort of stuff. Type netmath. Hit return. A small window, then a big window appear. Click on the large window. Center by clicking in the upper corner, clicking the cursor on "move" and adjusting the window until you can see both sides. Click on course materials (for ordinary differential equations.) Click on direction field stuff. Read the entire page once. You can move around the page by using the bar on the right. Modify the first equation to read plotdf -ode {d(y,x) = -.5*y + 6.3}. Class....apologies. This was the original equation. I did change it in the computer homework last Thursday. Click twice on the blue. Click on about (0,2). Can you figure out what is happening? Where is the steady state (equilibrium) solution? You are not looking at all the interesting parts. Move the mouse over to the upper left-hand corner. A ghost menu will appear. Click on CONFIG. A read menu will appear. We are interested in solutions that go forward in time, so change both to forward. We also need to see the steady state solution at about 12, and we really do not care at all about the part of y that is negative, so change the center of y to be at 9 (it looks silly to make it 10). Then click on OK and hit replot. Better? Y0u may want shorten the x radius and y radius and move the axes. over as well. If you want to see more of the curve, change the 100 to (say) 200. If you want more accuracy,you shorten the time-step, but add more steps! You get the idea. Playing with the ZOOM is fun. Shift ZOOM unzooms. By the way, you can get directions by turning the HELP toggle on. But be sure to turn it off before you print (the little balloons print, too!). To print your graph, once it is beautiful, click on CONFIG again, and then on print options. Turn the printer toggle to red. You may want to check with a lab proctor that your address for printing is correct. Hit OK twice and SAVE will now be PRINT. Click once, and look for your output at the printer. Get rid of the plot and start again by clicking DISMISS. Now you are back where you started. If you make a real mess, dismiss netmath and start again. The changes you have made are gone and correct programs are back. And so forth for the rest of the direction fields. To get a direction field for problem 5, you want to go half-way down the same page and look at the first system. Just modify it to be the one you want, although you may, again, have to adjust some parameters in the same way, using the CONFIG box, as you did the for the equation. In problems 1 and 2, you are asked to use a symbolic manipulator as well (twice is enough!). Dismiss your last graph and hit BACK at the menu at the top. You should see the main 427K page again. Hit the third option, which is Solving ODE's symbolically. Read the page once. Remember that this page solves a lot of ODE's for you. Go to any of the first blue equations. Change it to read: ode2('diff(y,x) = -.5*y + 6.3, y,x) The area below will turn pink while you do this. Hit return. Either you will be told you made an error (forget a *, a comma, a ) and all is lost) or the answer will be displayed. It should not take you long to do the two problems, but you might want to do an initial condition bit at the same time. Don't print these solutions. Copy them. To solve an initial condition problem, modify either the equation you are looking, or the one lower down on the page which is an initial condition problem for a second order equation. Choose your favorite name (Professor Schelter uses soln, I'll use key). Type (key:ode2('diff(y,x)= -.5*y + +6.3,y,x), tmp:IC1(key,x=0,y=2)) Check your parentheses, stars, commas, etc and press return! Good luck!