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Data/Sink/Graph

Introduction

Data sinks are generally used to catch the output of a model. There are three forms of data sink: text-based sinks, tabular sinks and graph sinks (described here). In the case of graph sinks, messages are interpreted as data-points to be graphed, and the sink's contents can be displayed as a graph.

Graph sinks are able to display multiple data sets in a variety of styles. They expect to receive two kinds of messages: type(DataSet, Type, Properties) and data(DataSet, X, Y). A type/3 term specifies the style or type of graph to be drawn for a given data set. The first argument is the name of the data set. The second argument is the graph type (either scatter, line, or bar. The third argument species graph properties such as colour and marker style. Individual data points are added to the graph by sending data/3 messages to the sink. Again, the first argument species the data set. The second and third argument specify a data point in horizontal (X) and vertical (Y) coordinates. (See also Graph Buffer.)

There is no limit to the number of data sets you can represent in one graph sink, and no limit in the number of data sinks you can have in one model. Multiple data sets within a single graph sink will be treated independently, with the limitation that the graph axes and labels are determined by graph properties, and are hence shared by all data sets within a graph. Multiple data sinks will behave as independent devices.

Secondary Properties

The third argument of each type/3 clause within a graph sink specifies secondary properties relating to the appearance of the graph. The secondary properties (similar to secondary properties in analogue buffers) allow specification of colour, fill style, and marker type. Thus, a histogram (using blue filled bars to represent frequency information) may be drawn by sending elements such as the following to a graph sink:

To draw a line graph using red filled square markers (and a red line) may be drawn by replacing the first element with:

Currently only three kinds of secondary property are recognised (colour, fill, and marker). There are four marker types (square, circle, cross and plus).

A graph sink may only contain one type definition for each data set. If a type definition is entered into a graph sink for a previously defined data set, the new definition will over-write the previous definition.

The Graph View

Graphical sinks may be viewed as graphs by selecting the "Current Graph" view. Each data/3 element is used to construct a data point on the graph for a particular data set, with the second and third arguments specifying the coordinates (and the first argument specifying the data set). The standard printing procedures may be used to print these tables.

Properties

Tabular data sinks have twelve properties:


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