set fit logfile "linearfit.log"
seed = rand(time(0))
unset key
set table "linearfit.dat"
f(x,a,b) = a*x + b
A = 2.2; B = 3.5
plot f(x,A,B) + 3*(rand(0) - 0.5)
unset table

fit f(x,a,b) "linearfit.dat" via a,b
set title sprintf("推定直線: y = %.3fx + %.3f", a, b) font "IPAGothic,16"
set grid
set term pngcairo enh font "Times,10" size 480,360
set out "fit_linear.png"
plot "linearfit.dat" pt 6 ps 0.4 lc rgb "#009900", f(x,a,b) lt 1