set polar
unset tics
set rtics format ""
set grid polar
set border 0 lt 0        # raxis の線種を破線にする
set term pngcairo enh font "Arial,10" size 480,480
set out "polar_alpha.png"
set size ratio -1
set samp 200
set title "alpha channel is available > ver. 4.7" font ",18"
plot cos(2.5*t)**2 w filledc lc rgb "#80ff3333", \
     sin(2.5*t)**2 w filledc lc rgb "#80cc0099"