The Koch snowflake (also known as the Koch curve, Koch star, or Koch island[1] [2]) is a fractal curve and one of the earliest fractals to have been described. It is based on the Koch curve, which appeared in a 1904 paper titled "On a Continuous Curve Without Tangents, Constructible from Elementary Geometry"[3] by the Swedish mathematician Helge von Koch.
The Koch snowflake can be built up iteratively, in a sequence of stages. The first stage is an equilateral triangle, and each successive stage is formed by adding outward bends to each side of the previous stage, making smaller equilateral triangles. The areas enclosed by the successive stages in the construction of the snowflake converge to
\tfrac{8}{5}
The Koch snowflake has been constructed as an example of a continuous curve where drawing a tangent line to any point is impossible. Unlike the earlier Weierstrass function where the proof was purely analytical, the Koch snowflake was created to be possible to geometrically represent at the time, so that this property could also be seen through "naive intuition".[3]
The Koch snowflake can be constructed by starting with an equilateral triangle, then recursively altering each line segment as follows:
The first iteration of this process produces the outline of a hexagram.
The Koch snowflake is the limit approached as the above steps are followed indefinitely. The Koch curve originally described by Helge von Koch is constructed using only one of the three sides of the original triangle. In other words, three Koch curves make a Koch snowflake.
A Koch curve–based representation of a nominally flat surface can similarly be created by repeatedly segmenting each line in a sawtooth pattern of segments with a given angle.[4]
Each iteration multiplies the number of sides in the Koch snowflake by four, so the number of sides after
n
If the original equilateral triangle has sides of length
s
n
an inverse power of three multiple of the original length.The perimeter of the snowflake after
n
The Koch curve has an infinite length, because the total length of the curve increases by a factor of
\tfrac{4}{3}
\tfrac{1}{3}
n
(\tfrac{4}{3})n
n
As the number of iterations tends to infinity, the limit of the perimeter is:
since
\tfrac{4}{3}>1
An
\tfrac{ln4}{ln3}
In each iteration a new triangle is added on each side of the previous iteration, so the number of new triangles added in iteration
n
The area of each new triangle added in an iteration is
\tfrac{1}{9}
n
where
a0
n
The total area of the snowflake after
n
Collapsing the geometric sum gives:
The limit of the area is:
since
\tfrac{4}{9}<1
Thus, the area of the Koch snowflake is
\tfrac{8}{5}
s
The volume of the solid of revolution of the Koch snowflake about an axis of symmetry of the initiating equilateral triangle of unit side is
| 11\sqrt{3 | |
The Koch snowflake is self-replicating with six smaller copies surrounding one larger copy at the center. Hence, it is an irrep-7 irrep-tile (see Rep-tile for discussion).
The fractal dimension of the Koch curve is
\tfrac{ln4}{ln3} ≈ 1.26186
=1
=2
It is impossible to draw a tangent line to any point of the curve.
The Koch curve arises as a special case of a de Rham curve. The de Rham curves are mappings of Cantor space into the plane, usually arranged so as to form a continuous curve. Every point on a continuous de Rham curve corresponds to a real number in the unit interval. For the Koch curve, the tips of the snowflake correspond to the dyadic rationals: each tip can be uniquely labeled with a distinct dyadic rational.
It is possible to tessellate the plane by copies of Koch snowflakes in two different sizes. However, such a tessellation is not possible using only snowflakes of one size. Since each Koch snowflake in the tessellation can be subdivided into seven smaller snowflakes of two different sizes, it is also possible to find tessellations that use more than two sizes at once.[8] Koch snowflakes and Koch antisnowflakes of the same size may be used to tile the plane.
A turtle graphic is the curve that is generated if an automaton is programmed with a sequence.If the Thue–Morse sequence members are used in order to select program states:
t(n)=0
t(n)=1
\tfrac{\pi}{3}
the resulting curve converges to the Koch snowflake.
The Koch curve can be expressed by the following rewrite system (Lindenmayer system):
Alphabet : F
Constants : +, −
Axiom : F
Production rules:
F → F+F--F+F
Here, F means "draw forward", - means "turn right 60°", and + means "turn left 60°".
To create the Koch snowflake, one would use F--F--F (an equilateral triangle) as the axiom.
Following von Koch's concept, several variants of the Koch curve were designed, considering right angles (quadratic), other angles (Cesàro), circles and polyhedra and their extensions to higher dimensions (Sphereflake and Kochcube, respectively)
Squares can be used to generate similar fractal curves. Starting with a unit square and adding to each side at each iteration a square with dimension one third of the squares in the previous iteration, it can be shown that both the length of the perimeter and the total area are determined by geometric progressions. The progression for the area converges to
2
\tfrac{\pi}{4}
The total area covered at the
n
while the total length of the perimeter is:which approaches infinity as
n
In addition to the curve, the paper by Helge von Koch that has established the Koch curve shows a variation of the curve as an example of a continuous everywhere yet nowhere differentiable function that was possible to represent geometrically at the time. From the base straight line, represented as AB, the graph can be drawn by recursively applying the following on each line segment:
| CE\sqrt{3 | |
Each point of AB can be shown to converge to a single height. If
y=\phi(x)
\phi(x)