Syntax:
set dummy {<dummy-var>} {,<dummy-var>}
show dummy
By default, gnuplot assumes that the independent, or "dummy", variable for the plot command is "t" if in parametric or polar mode, or "x" otherwise. Similarly the independent variables for the splot command are "u" and "v" in parametric mode (splot cannot be used in polar mode), or "x" and "y" otherwise.
It may be more convenient to call a dummy variable by a more physically meaningful or conventional name. For example, when plotting time functions:
set dummy t
plot sin(t), cos(t)
At least one dummy variable must be set on the command; set dummy by itself will generate an error message.
Examples:
set dummy u,v
set dummy ,s
The second example sets the second variable to s.