# set terminal pngcairo  font "arial,8" size 500, 300 
# set output 'circles.2.png'
unset key
set size ratio -1 1,1
set title "Trace of unconstrained optimization with trust-region method" 
set rrange [ * : * ] noreverse nowriteback  # (currently [8.98847e+307:-8.98847e+307] )
set trange [ * : * ] noreverse nowriteback  # (currently [-5.00000:5.00000] )
set xrange [ -2.50000 : 1.50000 ] noreverse nowriteback
set x2range [ * : * ] noreverse nowriteback  # (currently [-2.50000:1.50000] )
set yrange [ -1.00000 : 2.50000 ] noreverse nowriteback
set y2range [ * : * ] noreverse nowriteback  # (currently [-1.00000:2.50000] )
plot 'optimize.dat' with circles lc rgb "blue" fs transparent solid 0.15,     'optimize.dat' u 1:2 with linespoints lw 2 lc rgb "black"