'Program MANCHAOS.BAS plots the Mandelbrot set with colors for different
'periods and black for aperiodic (chaotic) orbits (period > nb%).
'Compile this program with PowerBASIC (http://www.powerbasic.com/)
'(c) 1997 by J. C. Sprott (http://sprott.physics.wisc.edu/)
screen 12
defext a-z
nb%=16000    'Bailout number (also highest period checked)
dim x!(nb%),y!(nb%)
for i%=0 to 639
    a=-2.1+(8/3)*i%/640
    if inkey$<>"" then end
    for j%=0 to 240
        b=1-2*j%/480
        c%=15
        x=a
        y=b
        for k%=0 to nb%
            xnew=x*x-y*y+a
            ynew=2*x*y+b
            if csng(xnew)=csng(x) and csng(ynew)=csng(y) then
                c%=1
                exit for
            end if
            x!(k%)=x: y!(k%)=y
            x=xnew
            y=ynew
            if x*x+y*y>4 then exit for
            if k%=nb% then
                found%=0: c%=0
                for l%=nb% to 1 step -1
                    if x!(l%)=csng(x) and y!(l%)=csng(y) then
                        c%=2+((nb%-l%) mod 13)
                        exit for
                    end if
                next l%
            end if
        next k%
        pset(i%,j%),c%: pset(i%,480-j%),c%
    next j%
next i%
line(0,0)-(639,479),0,b
while inkey$="": wend
end