Determining the indices of the x and y variables of the current plot
plot_indices(zargs)A numeric(2) containing the indices of the x and y variables to
be plotted in the current plot (the plot with number num). If
the current plot is a 2d plot, the same variable is used twice.
This is an auxiliary function useful, for example, when writing user-provided 1d and 2d plot functions.
Other tools for constructing your own plot1d and plot2d functions: burst_aux,
burst, check_zargs,
extract_1d, extract_2d