函数标记点，加箭头

clear
set obs 1
gen x=0.1
gen y=0.5*0.1-0.1*0.1+1.7
tw function y=0.5*x-1*x*x+1.7 ,range(0 0.4) text(1.736 0.12 "北京")
addplot:sc y x || pcarrowi 1.737 0.115 1.7394 0.1025