The computer demonstrations are all written around a common interface so that certain tasks can be executed in a manner that is similar in all the demonstrations. The common features include menus, mouse input, parameter input, function input and printing. These features are described later in this general introduction. First a few remarks are made on the structure of the documentation and on getting the machines running.

Documentation

The documentation for all demonstrations follows the same pattern and is divided into 5 sections. §1 describes the mathematical model behind the demonstration. §2 gives straightforward instructions for running it. §3 gives details of conditions that are required for the demonstration to run satisfactorily and of possible ways in which it may break down or show anomalous behaviour. A more exhaustive list of the options available in the demonstration is given in §4. A suggested strategy for using the demonstration and some discussion of fluid-dynamical ideas that it is intended to illustrate is given in §5. In some demonstrations references are added at the end, mainly for the benefit of those who are particularly interested in the topic in question and who may wish to read further about it.

List of Demonstrations

1: Irrotational coffee
2: Advection-diffusion
3: Random straining
4: Chaotic advection
5: Point vortices (unbounded, semi-infinite and periodic domains)
6: The Kida vortex
7: Vorticity contour - (a) patch, (b) strip.
8: Linearised contour equations
9: Shear flow instability
10: Rossby adjustment
11: Stratified shear flow instability
12: Linear Rossby wave propagation
13: Wind forced ocean currents
14: The Eliassen problem on the -plane
15: Axisymmetric potential vorticity inversion
16: Ellipsoidal vortex
17: Height-longitude Rossby wave dispersion
18: The equatorial QBO

Copyright

This notes are a guide to software that has been produced at University of Cambridge Department of Applied Mathematics and Theoretical Physics for the annual summer school in Geophysical and Environmental Fluid Dynamics (sponsored by the UK Natural Environment Research Council).
Copyright on software and notes is held by University of Cambridge.

Starting up

First switch on the monitor. (If necessary, switch on the computer using the large button on the front of the box.) The screen will eventually request that the three keys Ctrl-Alt-Del are pressed simultaneously to get to the login prompt.

At the login prompt enter the user id and password assigned to you. If you have make an error whilst typing the password (or indeed have used an incorrect user id) a pop-up window will indicate the error. Once you have logged on successfully, there will be a delay whilst software is loaded from the network. Eventually you will arrive at the Windows 2000 interface.

To access the GEFD summer school software click the `Start' icon at the bottom left-hand side of the screen, then select `Programs', then `Command Prompt', which will give an MS-DOS window, with the prompt ``F:$\backslash >$''. Type ``i:$\backslash$catam$\backslash$gefd'', which should deliver you to the main demonstration menu.

The main menu

Change the highlighted option by using the up and down arrow keys and press enter to select the currently highlighted option.

Pressing the <ESC> key at this stage will take you back to the system prompt which is useful only if you want to finish your session (see later).

Menu bars

All of the demonstrations are driven by a system of menu bars. You will notice a number of options, one of which is highlighted; this is the current option. There are two sorts of options on the menu bar, those that perform actions (action options) and those that lead to another menu (submenu options). The current option can be changed by pressing the left and right arrow keys. Pressing the down arrow key whilst on an action option does nothing, but on a submenu option it selects the new menu. You can move back to the previous menu by pressing the up arrow key or the <ESC> key. Pressing <ENTER> on an action option performs that action and on a submenu option it selects the submenu.

Parameter changing

Most of the demonstrations have a number of parameters that control the action of the program. Some of these parameters are grouped together in boxes. When the relevant menu option is chosen one of the parameters will have a field highlighted in red, this field can be moved using the up and down arrow keys. The left and right arrow keys move the cursor around the text of the field. There are two keys to delete text, <BACKSPACE> which deletes to the left of the cursor and <DELETE> which deletes the character under the cursor. The alphanumeric keys insert text into the field which scrolls to accommodate long input. Once you are satisfied with the input press <ENTER> to tell the machine to change the value. If however the value you have typed is not acceptable the machine will beep and you will be prompted to enter a new value. When you have changed the fields to your (and the machine's) satisfaction press <ESC> to return to the menu.

In some cases there is a small set of options for a parameter (e.g. a set of different timestepping methods). You can cycle through the options using the left or right arrow keys until the required option appears. Then pressing <ESC> or <ENTER> passes the parameter value to the program and returns you to the menu.

Some of the demonstrations have boxes that contain only one parameter. Pressing <ENTER> after changing the value will return you immediately to the menu (assuming the value is acceptable).

Mouse input

When the machine is expecting mouse input there will be a pointer on the screen. To draw a line the left mouse button must be depressed. If the left button is released the pointer will be rooted to the last point of input, by pressing the <BACKSPACE> key the line can be deleted. Input is terminated by pressing the right hand mouse button.

Function input

A number of demonstrations allow you to input curves in functional form. In these a window will pop up asking for a formula for a function of a particular variable or variables. Text is input and edited in exactly the same way as for the parameters above. Pressing <ENTER> will confirm your choice of formula. If however you have used something that the machine does not know about or there is an error in the syntax it will complain and prompt you again. If you decide not to input a formula pressing <ESC> will return you to the menu.

The demonstrations accept a fairly wide vocabulary of functions including sin(), cos(), tan(), asin(), acos(), atan(), sinh(), cosh(), tanh(), exp(), log(), sqrt(), abs(), min() and max(). The last two require two arguments. In addition the two constants pi and e are defined. There are some additional functions available whose definitions follow:

pow(): $pow(x,y)=x^y$.

gauss(): $gauss(x)=e^{-x^{2}}$.

H(): $H(x)= 0 ~ \{ x<0 \} , =1 ~ \{x \ge 0 \}$ (step function).

notch() $notch(x)= 0 ~ \{ x<-1 \}, = 1 ~ \{ -1 < x < 1 \}, = 0 ~ \{ 1 < x \}$. ( ``tophat'' function.)

tent(): $tent(x)= 0 ~ \{ x<-1 \}, = 1+x ~ \{ -1 < x < 0 \}, = 1-x ~ \{ 0 < x < 1 \}, = 0 ~ \{ 1 < x \}$.

rayleigh(): $rayleigh(x) = = -0.99+0.01x ~ \{ x<-1 \}, = x ~ \{ -1 < x < 1 \}, = 0.99+0.01x ~ \{ 1 < x \}$ ( rayl may be used as a synonym. This function may be useful in the shear instability demonstration.)

lessthan(): $lessthan(x,y)=1 ~ \{x \le y\}, =0 ~ \{x > y \}$.

morethan(): $morethan(x,y)=1 ~ \{x \ge y\}, =0 ~ \{x < y \}$.

gauss2(): $gauss2(x,y)=e^{-(x^{2}+y^{2})}$.

Printing

Many of the demonstrations allow the graphical content of the screen to be printed by selecting the Print option. This will tie up your machine for a minute or so, whilst the screen is dumped to the printer. You will then be able to resume normal working, though your printout may take some time to appear, particularly if a large print queue has built up.

What to do if a demonstration crashes

A demonstration could crash for a number of reasons and in a number of ways. In all cases it would be helpful if you could notify one of the supervisors since it may be possible to fix any bugs on the spot. It is possible that for certain values of input the numerical routines will fail. Where possible the programs have been written to recover gracefully from such errors, but a few may return you to the system prompt. In such cases typing ``gefd'' will restart the main menu.

If the machine seems to ignore keyboard and mouse input you will need to reset the machine by pressing <CTRL>, <ALT> and <DELETE> simultaneously and log in again. If this fails then there is nothing for it but to switch the machine off, wait for 10 seconds and then switch the machine on. It is most important that you wait before switching the machine on since the hard disk must be at rest before power up.

Finishing

All of the demonstrations have an Exit option which will take you back to the main menu. Once at the main menu press <ESC> to leave and then at the ``F:$\backslash >$'' press the three keys Ctrl-Alt-Del simultaneously to logout. Leave the computer on when you have finished with it, but switch off the monitor.

Comments

A lot of time and effort has been put in to make the demonstrations easy to use. However if you have found any particular features that are annoying or simply baffling please let us know so that we can incorporate improvements into future versions.