This demo displays the straight line given by X(t) = A + tC. To change
A or C, type the expression for the desired vector into the appropriate
text box in the control window and press Enter. The expression should
be of the form (x-coordinate, y-coordinate) (e.g., (1,2)). To move the
point X(t_{0}) along the line, use the following keys on the
appropriate line in the control window:

[<]: Decrease t_{0} by one step.

[>]: Increase t_{0} by one step.

[<<]: Decrease t_{0} until it reaches its minimum value.

[>>]: Increase t_{0} until it reaches its maximum value.

By default, the demo shows the point tracing out the curve, so that
only part of it is shown. To show the entire curve, check the box "Show
entire curve" by clicking on it. Click on the "Show position vector X(t_{0})"
box to show the position vector X(t_{0}) whose components
are the coordinates of the point X(t_{0}). To color the curve by t,
click on the box "Show Color Spectrum".