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Ziyaretçi defteri
 

Pentaflake

 
Pentaflake

A fractal with 5-fold symmetry. As illustrated above, five pentagons can be arranged around an identical pentagon to form the first iteration of the pentaflake. This cluster of six pentagons has the shape of a pentagon with five triangular wedges removed. This construction was first noticed by Albrecht Dürer (Dixon 1991).

PentaflakeDistances

For a pentagon of side length 1, the first ring of pentagons has centers at radius

 d_1=2r=1/2(1+sqrt(5))R=phiR,
(1)

where phi is the golden ratio. The inradius r and circumradius R are related by

 r=Rcos(1/5pi)=1/4(sqrt(5)+1)R,
(2)

and these are related to the side length s by

 s=2sqrt(R^2-r^2)=1/2Rsqrt(10-2sqrt(5)).
(3)

The height h is

 h=ssin(2/5pi)=1/4ssqrt(10+2sqrt(5))=1/2sqrt(5)R,
(4)

giving a radius of the second ring as

 d_2=2(R+h)=(2+sqrt(5))R=phi^3R.
(5)

Continuing, the nth pentagon ring is located at

 d_n=phi^(2n-1).
(6)

Now, the length of the side of the first pentagon compound is given by

 s_2=2sqrt((2r+R)^2-(h+R)^2)=Rsqrt(5+2sqrt(5)),
(7)

so the ratio of side lengths of the original pentagon to that of the compound is

 (s_2)/s=(Rsqrt(5+2sqrt(5)))/(1/2Rsqrt(10-2sqrt(5)))=1+phi.
(8)

We can now calculate the dimension of the pentaflake fractal. Let N_n be the number of black pentagons and L_n the length of side of a pentagon after the n iteration,

N_n = 6^n
(9)
L_n = (1+phi)^(-n).
(10)

The capacity dimension is therefore

d_(cap) = -lim_(n->infty)(lnN_n)/(lnL_n)
(11)
= (ln6)/(ln(1+phi))
(12)
= 1.861715...
(13)

(Sloane's A113212).

PentaflakeRecursiveGrowth

An attractive variation obtained by recursive construction of pentagons is illustrated above (Aigner et al. 1991; Zeitler 2002; Trott 2004, pp. 21-22).

 

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