I would like to ask whether it is possible, within the gnuplot command in Gretl, to assign multiple series to the secondary y-axis. In the example script below, the aim is to plot both heating and gasoline prices on the y2 axis. I tried using a list of variables in the y2 option, but it does not work as expected. Is there a way to specify more than one series for y2 using the gnuplot command? Any suggestions or workarounds would be greatly appreciated.

include yahoo_get.gfn

series wti = yahoo_price("CL=F",1)

series brent = yahoo_price("BZ=F",1)

series gasoline = yahoo_price("RB=F",1)

series heating = yahoo_price("HO=F",1)

list Energy = wti brent gasoline heating

list y2 = gasoline heating

gnuplot Energy --time-series --with-lines --output=display --y2axis=gasoline