## Tuesday, November 4, 2014

### Tic-Tac-Toe (井字遊戲)

Let f(a,b,x,y) = 1/exp(1/(a² - x²)²) + 1/exp(1/(a² - y²)²) - b

Equations:

Blue grid (#) ..... f(2, 0.999, x, y) = 0
Green nought (o) ..... f(0.125, 0.85, x, y) = 0
Red cross (x) ..... f(0.125, 0.999, 2(y+x), 2(y-x)) = 0

(Tessellations)

When the parameter 'a' changes from 0 to 2, the graph
changes shape from a plus sign(+) to a number sign(#).

In order to avoid discontinuities, we redefine f as follows:
f(a,b,x,y) = 1/exp(1/(s + (a² - x²)²)) + 1/exp(1/(s + (a² - y²)²)) - b,
where s(=0.001) is a small positive number.

Graph example:

( Mathematical software used: Graph )

## Sunday, August 17, 2014

### (5) Logarithmic spiral

( Mathematical software used: gnuplot )

## Sunday, August 10, 2014

### (1) Archimedean spiral: r(θ) = a*θ

(1 < number of spiral turns < 2)

(2 < number of spiral turns < 3)

### (2) Fermat's spiral (Parabolic spiral): r(θ) = a*sqrt(θ)

(1 < number of spiral turns < 2)

(2 < number of spiral turns < 3)

### (5) Logarithmic spiral: r(θ) = a*exp(b*θ)

(b = 0.25)

(b = 0.618)

( Mathematical software used: GeoGebra )

## Friday, August 8, 2014

### Spiral of Spirals

Spirals (green, magenta) around a Spiral Dodecaskelion (grey)

(GIF animation)

A spiral of spirals of spirals.
The spirals are logarithmic spirals: r(θ) = a exp(bθ), b = 0.2.

Spirals of spirals of spirals of ..... (b = 0.2)

A spiral of spirals of spirals.
The spirals are logarithmic spirals with b = 0.30635.

Spirals of spirals of spirals of ..... (b = 0.30635)

Logarithmic spirals
The pair of big spirals: b = 0.1
The small spirals: b = 0.2

The small logarithmic spirals: b = 0.5

The small logarithmic spirals: b = 0.2, 0.5

The small logarithmic spirals: b = 0.5, 0.8

The spirals are Archimedean spirals.
Small spirals: 1 < number of spiral turns < 2

The spirals are Archimedean spirals.
Small spirals: 2 < number of spiral turns < 3

( Mathematical softwares used: GeoGebra, gnuplot )

## Friday, July 25, 2014

The spirals are logarithmic spirals:
r(θ) = a exp(bθ), b = 0.25.

The spirals are logarithmic spirals:
r(θ) = a exp(bθ), b = golden ratio ~ 0.618.

The spirals are Archimedean spirals.
(1 < number of spiral turns < 2)

The spirals are Archimedean spirals.
(2 < number of spiral turns < 3)

The spirals are logarithmic spirals:
r(θ) = a exp(bθ), b = 0.05, 0.1, 0.15, 0.2, ..., 0.8.

( Mathematical software used: GeoGebra )

## Thursday, July 24, 2014

### Spiral Starfish - a logarithmic spiral pentaskelion (螺旋海星)

A pentaskelion with five logarithmic spirals r(θ) = a*exp(b*θ),
b ~ 0.30635 (same as that of the golden spiral).

b = 0.25

b = 0.5

b = golden ratio ~ 0.618

( Mathematical software used: gnuplot )

## Friday, July 11, 2014

### Grid Art using Equations and Inequalities

( Mathematical software used: Graph )