\
set terminal png;\
set output "erf.pyxplot.png";\
set key top left;\
set tics out;\
set xlabel "x";\
set ylabel "y";\
set title "Error function";\
plot \
 "out.data.txt" using 1:2 with line title "erf from math.h"\
,"out.data.txt" using 1:3 with line title "gsl-sf-erf"\
,"out.data.txt" using 1:4 with line title "myerf"\
,"input.data.txt" using 1:2 with points pointtype 2 title "tabulated data"\