\
set term pdf;\
set out "Fig.pdf";\
set key left;\
set xlabel "$x$";\
set ylabel "$y$";\
set title "Least-squares fit";\
plot \
 "out.data.txt" index 0 with errorbars title "data"\
,"out.data.txt" index 1 with lines title "$F_{\vec c}(x)\doteq c_0+c_1x+c_2x^2$"\
,"out.data.txt" index 2 with lines title "$F_{\vec{c}+\Delta\vec{c}}(x)$"\
,"out.data.txt" index 3 with lines title "$F_{\vec{c}-\Delta\vec{c}}(x)$"\