Hi, When I try to use : set_plot_option(['t,-%pi,%pi]); or set_plot_option([t,-%pi,%pi]); I got the same error : (%i211) set_plot_option(['t,-%pi,%pi]); -%pi is not of the right type in t list -- an error. To debug this try debugmode(true); I must use : set_plot_option([gnuplot_preamble, "set trange [-pi:pi]"])$ Why ? Adam