Polar Plots

To make polar plots of expressions use the Set > Coordinate System command162L784 to select the polar coordinate system. See the on-line help for that command for a summary of how plots of expressions and equations are interpreted in polar coordinates.

In polar coordinates the 2D-plot window's Insert > Plot commandB2C2._ prompts you to enter information into the Parametric Plot ParametersParametric_Plot_Parameters dialog box.

In polar coordinates the position of the cross is displayed in polar coordinates on the status bar. The radial distance of the cross from the origin is the first coordinate. The angle of the cross, represented in either radians or degrees depending on the angle mode, is measured counterclockwise from the positive x-axis and is the second coordinate.

Trace mode is available in both rectangular and polar coordinates. When you start tracing in polar coordinates, the cross goes to the midpoint of the parameter range. The midpoint of the parameter range is calculated from the value in the Points field when plotted in discrete mode. The midpoint of a continuous plot is calculated from the current value in the Points field.

When tracing plots in polar coordinates, the 2D-plot window title bar shows a message of the form

Tracing expression #n, at t = x.xxxxxxx

where n is the number of the expression being traced and x.xxxxxxx is the parameter value at the box location.

For tracing purposes, the angular range of the polar plot is divided into equally spaced points. The number of points is 10 times the number of points entered in the Parametric Plot ParametersParametric_Plot_Parameters dialog box. When tracing a polar plot, use the direction keys or mouse to move the box along the plot as follows:

• Left arrow or click the right mouse button and choose Move left one unit to decrease the parameter value to move the box the distance of one point along the plot.

• Right arrow or click the right mouse button and choose Move right one unit to increase the parameter value to move the box the distance of one point along the plot.

• Ctrl+Left arrow or click the right mouse button and choose Move left multiple units to decrease the parameter value to move the box the distance of ten points along the plot.

• Ctrl+Right arrow or click the right mouse button and choose Move right multiple units to increase the parameter value to move the box the distance of ten points along the plot.

The Up arrow and Down arrow keys as well as the mouse can be used to trace another rectangular or polar plot line in a 2D-plot window with multiple expressions plotted (see Multiple PlotsMultiple_Plots ).

Alternatively, the trace box may be moved to a specific location using the mouse. Simply click the left mouse button at the desired angular coordinate to move the box to the corresponding plot value at that coordinate.

The polar plot line only spans expression values from the minimum parameter to the maximum parameter specified. When tracing a polar plot, the box can be moved off the edge of the plot line in order to visualize the shape of the plot if the parameter range were extended.