# very slow! be patient
fx(a,x,n) = 0 < n ? fx(a,a*(1-x)*x,n-1): a*(1-x)*x

unset key
set samples 1600
set isosamples 100
set yrange [0:1]
set xrange [2.5:4]
set term pngc enh font "Arial,8" size 480,360
set out "logistic2.png"
set xlabel "a" font ",10"
set ylabel "x" font ",10"
plot '++' using (xa = fx($1,0.8,100), $1):(fx($1,xa,int($2*100))) w d