set xlabel 'simulation time'
set output "${PREF}.eps"

plot \
  "${PREF}.gr" using 1:2 w l lw 2 title 'red', \
  "${PREF}.gr" using 1:3 w l lw 2 title 'green', \
  "${PREF}.gr" using 1:4 w l lw 2 title 'blue'
EOF