Gnuplot use two different scales in the same axis - gnuplot

Question

I am trying to create a graphic using gnuplot 5.0 with two scales in the same x axis. I have managed to create one using the multiplot option with the following code:
reset
set terminal pngcairo
set output "test.png"
unset key
set ylabel "Temperature (C)"
set ytics nomirror
set yrange[0:7]
set multiplot layout 1,2
set xrange [0:5.99] #Avoid plotting the last xtics in the first graphic
set xlabel "Heating time (minutes)"
set rmargin at screen 0.7
plot x
set xrange [0:4]
set xlabel "Seconds after stop"
set rmargin
set lmargin at screen 0.7
set xtics 1
unset ylabel
unset ytics
set y2tics nomirror
set format y2 ''
f(x) = a * exp (-x*b)
a=6
b=1
plot f(x)
With this result:
I want to generate several images like this one and add them in a multiplot arrangement, but I am not sure if using nested multiplots will be easy. Is there an easier way to obtain each of the images without using multiplot, like splitting the xaxis in two components?
Thanks in advance.

Answer 1

Just in case this still might be of interest to the OP or somebody else... You don't explicitly write whether you want to plot functions or data from a datafile. In your examples you use functions.
You can do something without "nested" multiplots, which would certainly be possible as well, but probably getting a bit confusing.
So, maybe the following might be easier. You basically set the xtics "manually". In order to avoid typing the same code several times you can use macros (check help macros).
Code:
### multiplot graph with different x-axis scales
reset session
# define functions
Temperature(x) = x<t0 ? x*a/t0 : a*exp(-(x-t0)*b)
myColor(col) = column(col)<t0 ? 0xff0000 : 0x0000ff
myTic(x,t) = sprintf("%g", x<=t ? x : x-t)
# define macro
myPlot = "\
set xrange[0:t0+t1]; \
set arrow 1 from first t0, graph 0 to first t0, graph 1 nohead; \
set label 1 'heating' center at first t0/2., graph 0 offset 0,-2; \
set label 2 'cooling' center at first (t0+t1/2.), graph 0 offset 0,-2; \
set xtics (); \
do for [i=0:int(t0/dt1)] { set xtics add (myTic(i*dt1,t0) i*dt1) }; \
do for [i=0:int(t1/dt2)] { set xtics add (myTic(i*dt2,t1) i*dt2+t0) }; \
plot '+' u 1:(Temperature($1)):(myColor(1)) w l lc rgb var "
set samples 200
set key noautotitle
set bmargin 3
set ylabel "Temperature"
set grid x,y
set multiplot layout 2,2
t0=6; t1=4; dt1=1; dt2=1; a=6; b=1
#myPlot
t0=4; t1=10; dt1=1; dt2=2; a=4; b=0.5
#myPlot
t0=20; t1=30; dt1=5; dt2=10; a=2; b=0.1
#myPlot
t0=4; t1=4; dt1=1; dt2=1; a=10; b=1
#myPlot
unset multiplot
### end of code
Result: