The snowflake curve made its first appearence in a 1906 paper written by the Swedish mathematician Helge von Koch. It is a closed curve of infinite perimeter that encloses a finite area.
Start with a equallateral triangle of side length and area , the snowflake curve is constructed iteratively (see Fig. 1). At each iteration, an outward equallateral triangle is created in the middle third of each side. The base of the newly created triangle is removed:
Let be the number of sides the snowflak curve has at the end of iteration. From Fig. 2, we see that
Solving for (see Fig. 3) gives
Suppose at the end of iteration, the length of each side is , we have
and, , the perimeter of the snowflake curve at the end of iteration is
It follows that
Let be the area of equallateral triangle created at the end of and iteration respectively. Namely,
solving for gives
Hence, the area added at the end of iteration
After iterations, the total enclosed area
As the number of iterations tends to infinity,
i.e., the area of the snowflake is of the area of the original triangle.
If at each iteration, the new triangles are pointed inward, the anti-snowflake is generated (see Fig. 4 ).
Fig. 4 First four iterations of anti-snowflake curve
Like the Snowflake curve, the perimeter of the anti-snowflake curve grows boundlessly, whereas its total enclosed area approaches a finite limit (see Exercise-1).
Exercise-1 Let be the area of the original triangle. Show that the area encloded by the anti-snowflake curve approaches .
Exercise-2 An “anti-square curve” may be generated in a manner similar to that of the anti-snowflake curve (see Fig. 5). Find:
(1) The perimeter at the end of iteration
(2) The enclosed area at the end of iteration
Fig. 5 First four iterations of anti-square curve