7.1 Plot Basics

When Plot is applied, the active expression in the algebra display is added to the plot display. To add all the expressions in the algebra display, first touch the select-all icon in the menu bar. To add a set of expressions to the plot, first create a selection set using Select . The plotter will replace any expression already in the plot display if it has the same signature as an expression being added.

7.1.1 Expression Types

The plotter handles the following types of expression.

Function Definition

A real-valued function of a real for which all elaboration variables can be bound is evaluated to produce a sequence of x-y coordinates that can be plotted.

Variable Definition

A real variable is treated as an adjustable constant; an interactive control on the plotter display allows the defined value to be changed. Similarly, a composite variable is treated as an adjustable constant; it's interactive control has more than one degree of freedom. See §7.4

Protected Definition

A definition in a guard is not plotted but is made available for binding.

Equation

If the equation has a function on one side, the equation is treated as a function definition. If the equation has zero on one side, the other side is treated like a formula. If neither side is zero, a new expression in which one side is subtracted from the other side is created and treated as a formula.

Real Formula

The formula is examined for unbound variables. If there is exactly one, it is treated as the independent variable and the formula is treated as a function of that variable. If there is more than one, the formula should be rewritten as a function definition with an explicit parameter list so the unbound variables can be determined.

Composite

Composite expressions that can be evaluated to a constant value are plotted as position vectors. Composite expressions that can be evaluated to a single-valued function of composites are treated as tuple generators.

Tuple or tuple generator

If the expression is a tuple of points constructed from expressions that meet the criteria for plottable expression, the tuple is plotted as a sequence of line segments.

Set or set generator

If the expression is a set of plottable expressions, each item is treated as a separate plottable expression.

Note that for any expression containing a tuple of scalars, the tuple is replaced by a vector. Upon return from the plotter to the workspace, such expressions will be updated to reflect the change.

7.1.2 Adjusting the Plot

The default plot displays a horizontal axis from -1 to 1 and a vertical axis from -1 to 1. The axes are sensitive to drag actions at the extremities, the origin and midway between the origin and any extremity.

To change the extent of an axis	drag the extremity.
To change the scale of either axis	drag the midway.
To double the scale of all axes	double touch outside the axes area.
To move the plot on the display	drag the origin.
To reset the plot to the default configuration	double touch the origin.

The axes are decorated with tick marks and numerical indicators. The tick marks are at intervals that depend on the axes' extents. The density of tick marks changes logarithmically. Intervals of 1, 10, 100, ... are used.

Grid lines can be displayed at and between tick marks. To change whether axis and grid lines are displayed, use the display-grid button. The button cycles through three options: displays both axes and grid lines, displays neither axes nor grid lines and displays axes without grid lines. Grid lines are spaced at one-tenth the interval between numbered tick marks unless that would place them too close together to be useful.

7.1.3 Managing the Plot Display

To select an expression	touch it in the legend.
To deselect an expression	touch a selected expression.
To remove an expression	select it and touch
To protect or hide	select an expression and touch
To remove all expressions	touch then touch .

7.1.4 Saving the Plot Display

The plot display can be saved to a file in SVG or PNG format. This facility is available only in the desktop version of Myron. To save the plot display, use either of the SVG or PNG buttons in the menu bar. The buttons will not be visible unless the license contains the SVG capability. The files follow the same naming conventions as System SVG using the prefix “plot” (see §8.2.7).