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2 Level Three Programs

2.1 Introduction

These utility programs are supplied on cassette complete and ready to run. To use them, you do not need to read any more than this section of the manual, although they should serve as a good introduction to the sort of thing you can do using the lower-level programs. To load the programs, use the CHAIN or LOAD command in the usual way.

The best way to find out how to use these programs is to run one, but the following brief summary may help.

On starting up, two or three pages of control data are displayed a page at a time. The first page is to do with which mode is to be used for the eventual display, colours to be used, etc. At the foot of each page a prompt line gives you the chance to make changes to the data on that page (type C) or you can go on (press SPACE). If you ask to make changes, the page is displayed again, pausing after each line to allow you to set new values. If the old value is acceptable, type only a RETURN, otherwise type the new value and end it with RETURN. You can go on doing this until you are satisfied, then type RETURN by itself.

The last page says that the program is ready to start drawing the graphs (or whatever is appropriate) and gives a list of keys that you will be able to use to control the program. After you next press the SPACE bar, the screen is cleared, axes are usually drawn, and the program waits for you to hit one of the control keys. To help you remember which they are, the ? key will give a list of them (without explanations) which lasts for 5 seconds. Each control key puts up a prompt on the bottom line, which you must answer with one or more data items.

For example, in the bar chart utility L3-BAR, the SPACE bar prompts for data to draw the next bar as follows :

X,Y ?

to which you could reply, for example, '5,8', to put the next bar at horizontal position 5 with height 8.

Certain control keys apply to all the utilities. C allows you to select a logical colour (see the User Guide), L allows the logical colours to be redefined in terms of physical colours, and T asks for a title and a position on the screen to put it. This position is always expected in the units used to draw the display.

When your graph is complete or you want to abandon the program, escape will clear the screen and ask you if you want to repeat or stop.

2.2 List of Level Three Utilities

L3-BAR

Draws bar charts (histograms). The user defines each bar's position individually. It is possible to change the width, colour and offset of each bar, and to put a title on the chart.

Keys:

C: colour
L: change logical colours
B: bar base
O: offset
W: width
T: title
?: list of prompt keys

L3-GRA

Draws graphs (X-Y plots). The user may specify each point individually, or define a function which will be evaluated for a specified range of the X-axis and plotted, or any combination of these. The graph may be titled, colours changed, and if a function is used this may be written on the screen at any desired point. The function must be typed in as a valid BASIC expression in X.

Keys :

M: move to X,Y
D: draw to X,Y
C: colour
L: change logical colours
F: input function(X)
P: range to plot, no. of points
U: display function at X,Y
T: title
?: list of prompt keys

L3-CUR

Draws graphs like L3-GRA, but for function plotting allows X and Y to be defined as separate functions of a parameter T. Note that by setting the function X(T) to be just T, the program can be made to behave just like L3-GRA. Functions must be typed as valid BASIC expressions in terms of the variable T only.

Keys:

M: move to X,Y
D: draw to X,Y
C: colour
L: change logical colours
X: input function X(T)
Y: input function Y(T)
U: display X(T) at X,Y
V: display Y(T) at X,Y
P: T-range to plot, no. of points
T: title

L3-PIE

Draws pie charts. The user specifies the size of each sector in %. The starting angle of each sector is chosen automatically, but this can be over-ridden if required. Colours may be varied, and each sector labelled with its size in %.

Keys:

S: starting angle for next sector
D: draw next sector, size in %
C: colour
L: change logical colours
T: title
W: write sector size in colour 0 of the last sector drawn.
?: display list of prompt keys

L3-CV3D

Draws perspective graphs, otherwise like L3-CUR. Three functions X(T),Y(T), and Z(T) must be set, and/or individual points may be given.

Keys:

A: change viewing angles
M: move to X,Y,Z
D: draw to X,Y,Z
C: colour
L: change logical colours
X: input function X(T)
Y: input function Y(T)
Z: input function Z(T)
P: T-range to plot, no.
T: title
U: print X(T) at X,Y,Z
V: print Y (T)
W: print Z (T)
?: list of prompts

L3-CO2D

Draws contour maps on 'flat' axes. A function F(X,Y) needs T be set, and it must be a valid expression in BASIC involving X and Y only. The key P (for Plot) will ask for the range of contour heights that are to be drawn.

Keys :

C: colour
L: change logical colours
F: input function(X,Y)
P: plot for range of heights
T: title at X,Y
U: print fn at X,Y
?: print all recognised prompts

L3-CO3D

Draws contour maps in perspective. This program behaves in most respects like L3-CO2D except that perspective plots are produced. Because of the size of the program only modes 4 or 5 may be used.

Keys:

A: change view angles
M: move to X,Y,Z
D: draw to X,Y,Z
C: colour
L: change logical colours
F: input function F(X,Y)
P: plot contours
T: title
U: print F(X,Y) at X,Y,Z
?: list of prompts

L3-SURF

Draws a wireframe view of a function of two variables. This is an alternative method to L3-CO 3D of investigating such functions.

Keys:

A: change view angles
M: move to X,Y,Z
D: draw to X,Y,Z
C: colour
L: change logical colours
F: input function F(X,Y)
P: plot
T: title
U: print F(X,Y) at X,Y,Z
?: list of prompts

2.3 Using Level Three Utilities

The programs are large and use display mode 5 by default as this allows more memory for program than modes 1 or 2. However many of the programs can be successfully run in other modes.

Also concerning memory space, the contouring functions use an array, £W(I,J] to store function values. This is dimensioned as £W(10,10) by default, but the user may change this by modifying line 20 of the program to set IM%, JM% to other values.

If ESC is pressed, followed by a request to repeat program, any functions that were previously set preserved, but other values are not.

Note that by using the C key to draw in the background colour (0 by default) it is possible to selectively erase part of a graph or chart by drawing or plotting again over the part to be deleted.


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