Encyclopaedia Index


(used in AUTOPLOT)

If a plot contains several data elements, you may wish to distinguish them by using various kinds of dashed lines(see DASHED LINES). Alternatively, the data points of a data element may be shown individually as "blobs", and not be joined up at all. These requirements are met by the BLBn commands, which are used in precisely the same way as the plot command. The n in these commands represents a single digit and must not be preceded by a space. The value of n determines the type of blob to be used, as follows:

Some of the blobs generated by these commands may differ slightly, depending on the graphics terminal used.

Suppose you wish to plot three sets of data; the first drawn with solid lines, the second with dashed lines and the third with small circles at the data points. You achieve this by the following sequence of commands:

The final SCALE ensures that all of the data elements will be shown within the axis window. As another example, suppose that there is one data element to be shown by small circles, and three more all to be shown by finely-dashed lines. The following command sequence is now required:

Marking data points on a continuous curve

Suppose that an element has been represented by a solid curve, but that it is desired to mark on this curve the locations of the data points. The curve will have been drawn using the PLOT command. Subsequent use of BLOB for the same data element, without clearing the screen first, will achieve the desired result. It should be noted, however, that if the picture is now redrawn, the blobs will remain but the solid curve will vanish. This could be reinstated by use of PLOT; but the problem will recur every time a REDRAW is performed. This difficulty may be overcome by creating a second data element containing the same data as the first and using PLOT on one and BLOB on the other; the picture can then be redrawn perfectly.


(changing type of)

After plotting several elements, you may decide to change the type of dashed line or perhaps replace a solid line by blobs. This is easily accomplished. Suppose, for instance, that four elements have been drawn, all with solid lines, and that they are to be changed, respectively, to dashed lines of type 1 and 2 and blobs of types 2 and 3. The following command sequence will suffice:

DOT 1; DOT2 2; BLB2 3; BLB3 4;REDRAW