This module is part of the original MMBasic library. It is reproduced here with kind permission of Hugh Buckle and Geoff Graham. Be aware it may reference functionality which has changed or is deprecated in the latest versions of MMBasic.

100 'MANDELBROT.BAS - Draws mandelbrot set fractal images
102 'By loki on the Back Shed  Aug 2012
103 'See topic (MM) Mandelbrot & Julia set fractals
105 'Specify initial values
110 RealOffset = -2.0
115 ImaginOffset = -1.2
130 MAXIT=70 'max iterations
165 PixelWidth = MM.HRES
170 PixelHeight = MM.VRES
175 GAP = PixelHeight / PixelWidth
180 SIZE = 2.8
185 XDelta = SIZE / PixelWidth
190 YDelta = (SIZE * GAP) / PixelHeight
195 CLS
200 'Loop processing - visit every pixel in screen area and base colour of pixel
201 ' on the number of iterations required to escape boundary conditions
202 ' If count hits max iterations then pixel hasn't escaped and is part of the set (the 'inner sea')
205 FOR X = 0 TO (PixelWidth - 1)
210   Cx = X * Xdelta + RealOffset
215   FOR Y = 0 TO (PixelHeight - 1)
220     Cy = Y * YDelta + ImaginOffset
225     Zr = 0.0
230     Zi = 0.0
235     COUNT = 0
240     'Begin Iteration loop, checking boundary conditions on each loop      
250     DO WHILE (( COUNT <= MAXIT ) AND (( Zr * Zr + Zi * Zi ) <= 4 ))
255       new_Zr = Zr * Zr - Zi * Zi + Cx
260       new_Zi = 2 * Zr * Zi + Cy
265       Zr = new_Zr
270       Zi = new_Zi
275       COUNT = COUNT + 1
280     LOOP
415     PIXEL(X,Y) = ((COUNT MOD 2) - 1) * -1
500   NEXT Y
510 NEXT X
520 DO
530   a$ = INKEY$
540 LOOP WHILE a$ = ""
600 'End listing