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Functional Programming in TypeScript

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11 Apr 2024CPOL17 min read 16K   84   16   3
Functional Programming in TypeScript through Algebra, Numbers, Euclidean Plane and Fractals
This article discusses Functional Programming in TypeScript through Algebra, Numbers, Euclidean Plane and Fractals. A wide range of topics are covered related to functional programming and set operations. Code examples and explanations are provided to help readers understand the concepts and how to implement them in TypeScript.

Image 1

Contents

  1. Introduction
  2. TypeScript Environment
  3. Representing Data Through Functions
    1. Sets
    2. Binary Operations
    3. Go Further
  4. Euclidean Plane
    1. Drawing a Disk
    2. Drawing Horizontal and Vertical Half-planes
    3. Functions
    4. Go Further
  5. Fractals
    1. Complex Numbers and Drawing
    2. Mandelbrot Fractal
    3. Go Further
  6. History

Introduction

In TypeScript, functions are nothing but objects. Hence, functions can be constructed, passed as parameter, returned from functions or assigned into variables. Thus, TypeScript has first-class functions. More precisely, TypeScript supports the following:

  • Higher-order functions arguments
  • Higher-order functions results
  • Nested functions
  • Anonymous functions
  • Closures
  • Partial application (ECMAScript 5)

This article will not discuss the basics of functional programming, as you can find numerous resources on this topic on the Internet. Instead, it will talk about functional programming in TypeScript applied to algebra, numbers, the Euclidean plane, and fractals. The examples provided in this article will start from simple to more complex but always illustrated in a simple, straightforward and easy-to-understand manner.

TypeScript Environment

To run the source code, you'll need to install Node.js. Once Node.js is installed, download the source code archive, unzip it, go to the source code folder you unzipped on a terminal, set up TypeScript environment and install all necessary dependencies with the following command:

Shell
npm install

To run numbers' demo, run the following command:

Shell
npm run numbers

To run Euclidean plane's demo, run the following command:

Shell
npm run plane

To run fractals' demo, run the following command:

Shell
npm run fractals

Representing Data Through Functions

Let S be any set of elements a, b, c ... (for instance, the books on the table or the points of the Euclidean plane) and let S' be any subset of these elements (for instance, the green books on the table or the points in the circle of radius 1 centered at the origin of the Euclidean plane).

The Characteristic Function S'(x) of the set S' is a function which associates either true or false with each element x of S.

S'(x) = true if x is in S'
S'(x) = false if x is not in S'

Let S be the set of books on the table and let S' be the set of green books on the table. Let a and b be two green books, and let c and d be two red books on the table. Then:

S'(a) = S'(b) = true
S'(c) = S'(d) = false

Let S be the set of the points in the Euclidean plane and let S' be the set of the points in the circle of radius 1 centered at the origin of the Euclidean plane (0, 0) (unit circle). Let a and b be two points in the unit circle, and let c and d be two points in a circle of radius 2 centered at the origin of the Euclidean plane. Then:

S'(a) = S'(b) = true
S'(c) = S'(d) = false

Thus, any set S' can always be represented by its Characteristic Function. A function that takes as argument an element and returns true if this element is in S', false otherwise. In other words, a set (abstract data type) can be represented through a function in TypeScript.

TypeScript
type Set<T> = (x: T) => boolean

In the next sections, we will see how to represent some fundamental sets in the algebra of sets through TypeScript in a functional way, then we will define generic binary operations on sets. We will then apply these operations on numbers then on subsets of the Euclidean plane. Sets are abstract data structures, the subsets of numbers and the subsets of the Euclidean plane are the representation of abstract data-structures, and finally the binary operations are the generic logics that works on any representation of the abstract data structures.

Sets

This section introduces the representation of some fundamental sets in the algebra of sets through TypeScript.

Empty set

Image 2

Let E be the empty set and Empty its Characteristic function. In algebra of sets, E is the unique set having no elements. Therefore, Empty can be defined as follows:

Empty(x) = false if x is in E
Empty(x) = false if x is not in E

Thus, the representation of E in TypeScript can be defined as follows:

TypeScript
const empty = <T>() => (e: T) => false

In algebra of sets, Empty is represented as follows:

Image 3

Thus, running the code below:

TypeScript
console.log('\nEmpty set:')
console.log('Is 7 in {}?', common.empty<number>()(7))

gives the following results:

Image 4

Set All

Image 5

Let S be a set and S' be the subset of S that contains all the elements and All its Characteristic function. In algebra of sets, S' is the full set that contains all the elements. Therefore, All can be defined like this:

All(x) = true if x is in S

Thus, the representation of S' in TypeScript can be defined as follows:

TypeScript
const all = <T>() => (e: T) => true

In algebra of sets, All is represented as follows:

Image 6

Thus, running the code below:

TypeScript
console.log('\nSet All:')
console.log('Is 7 in integers set?', common.all<number>()(7))

gives the following results:

Image 7

Singleton Set

Let E be the Singleton set and Singleton its Characteristic function. In algebra of sets, E also known as unit set, or 1-tuple is a set with exactly one element e. Therefore, Singleton can be defined as follows:

Singleton(x) = true if x is e
Singleton(x) = false if x is not e

Thus, the representation of E in TypeScript can be defined as follows:

TypeScript
const singleton = <T>(x: T) => (y: T) => x === y

Thus, running the code below:

TypeScript
console.log('\nSingleton set:')
console.log('Is 7 in the singleton set {0}?', common.singleton(0)(7))
console.log('Is 7 in the singleton set {7}?', common.singleton(7)(7))

gives the following results:

Image 8

Other Sets

This section presents subsets of the integers set.

Even Numbers

Let E be the set of even numbers and Even its Characteristic function. In mathematics, an even number is a number which is a multiple of two. Therefore, Even can be defined as follows:

Even(x) = true if x is a multiple of 2
Even(x) = false if x is not a multiple of 2

Thus, the representation of E in TypeScript can be defined as follows:

TypeScript
const even = (x: number) => x % 2 === 0

Thus, running the code below:

TypeScript
console.log('\nEven numbers set:')
console.log('Is 99 in even numbers set?', numbers.even(99))
console.log('Is 998 in even numbers set?', numbers.even(998))

gives the following results:

Image 9

Odd Numbers

Let E be the set of odd numbers and Odd its Characteristic function. In mathematics, an odd number is a number which is not a multiple of two. Therefore, Odd can be defined as follows:

Odd(x) = true if x is not a multiple of 2
Odd(x) = false if x is a multiple of 2

Thus, the representation of E in TypeScript can be defined as follows:

TypeScript
const odd = (x: number) => x % 2 === 1

Thus, running the code below:

TypeScript
console.log('\nOdd numbers set:')
console.log('Is 99 in odd numbers set?', numbers.odd(99))
console.log('Is 998 in odd numbers set?', numbers.odd(998))

gives the following results:

Image 10

Multiples of 3

Let E be the set of multiples of 3 and MultipleOfThree its Characteristic function. In mathematics, a multiple of 3 is a number divisible by 3. Therefore, MultipleOfThree can be defined as follows:

MultipleOfThree(x) = true if x is divisible by 3
MultipleOfThree(x) = false if x is not divisible by 3

Thus, the representation of E in TypeScript can be defined as follows:

TypeScript
const multipleOfThree = (x: number) => x % 3 === 0

Thus, running the code below:

TypeScript
console.log('\nMultiples of 3 set:')
console.log('Is 99 in multiples of 3 set?', numbers.multipleOfThree(99))
console.log('Is 998 in multiples of 3 set?', numbers.multipleOfThree(998))

gives the following results:

Image 11

Multiples of 5

Let E be the set of multiples of 5 and MultipleOfFive its Characteristic function. In mathematics, a multiple of 5 is a number divisible by 5. Therefore, MultipleOfFive can be defined as follows:

MultipleOfFive(x) = true if x is divisible by 5
MultipleOfFive(x) = false if x is not divisible by 5

Thus, the representation of E in TypeScript can be defined as follows:

TypeScript
const multipleOfFive = (x: number) => x % 5 === 0

Thus, running the code below:

TypeScript
console.log('\nMultiples of 5 set:')
console.log('Is 15 in multiples of 5 set?', numbers.multipleOfFive(15))
console.log('Is 998 in multiples of 5 set?', numbers.multipleOfFive(998))

gives the following results:

Image 12

Prime Numbers

A long time ago, when I was playing with Project Euler problems, I had to resolve the following one:

By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, 
we can see that the 6th prime is 13.
What is the 10 001st prime number?

To resolve this problem, I first had to write a fast algorithm that checks whether a given number is prime or not. Once the algorithm written, I wrote an iterative algorithm that iterates through primes until the 10 001st prime number was found.

Let E be the set of primes and Prime its Characteristic function. In mathematics, a prime is a natural number greater than 1 that has no positive divisors other than 1 and itself. Therefore, Prime can be defined as follows:

Prime(x) = true if x is prime
Prime(x) = false if x is not prime

Thus, the representation of E in TypeScript can be defined as follows:

TypeScript
const prime = (x: number) => {
  if (x <= 1) return false
  if (x < 4) return true
  if (x % 2 === 0) return false
  if (x < 9) return true
  if (x % 3 === 0) return false
  const sqrt = Math.sqrt(x)
  for (let i = 5; i <= sqrt; i += 6) {
    if (x % i === 0) return false
    if (x % (i + 2) === 0) return false
  }
  return true
}

Thus, running the code below to resolve our problem:

TypeScript
console.log('\nPrimes set:')
console.log('Is 2 in primes set?', numbers.prime(2))
console.log('Is 4 in primes set?', numbers.prime(4))
console.log('The 10 001st prime number is', numbers.getPrime(10001))

where getPrime is defined below:

TypeScript
const getPrime = (p: number) => {
  for (let i = 1, count = 0; ; i++) {
    if (prime(i)) count++
    if (count === p) return i
  }
}

gives the following results:

Image 13

Binary Operations

This section presents several fundamental operations for constructing new sets from given sets and for manipulating sets. Below the Ven diagram in the algebra of sets.

Image 14

Union

Image 15

Let E and F be two sets. The union of E and F, denoted by E U F is the set of all elements which are members of either E and F.

Let Union be the union operation. Thus, the Union operation can be implemented as follows in TypeScript:

TypeScript
const union = <T>(e: Set<T>, f: Set<T>) => (x: T) => e(x) || f(x)

Running the code below:

TypeScript
console.log('\nUnion:')
console.log('Is 7 in the union of Even and Odd Integers Set?', core.union(numbers.even, numbers.odd)(7))

gives the following results:

Image 16

Intersection

Image 17

Let E and F be two sets. The intersection of E and F, denoted by E n F is the set of all elements which are members of both E and F.

Let Intersection be the intersection operation. Thus, the Intersection operation can be implemented as follows in TypeScript:

TypeScript
const intersection = <T>(e: Set<T>, f: Set<T>) => (x: T) => e(x) && f(x)

Running the code below:

TypeScript
console.log('\nIntersection:')
const multiplesOfThreeAndFive = core.intersection(numbers.multipleOfThree, numbers.multipleOfFive)
console.log('Is 15 a multiple of 3 and 5?', multiplesOfThreeAndFive(15))
console.log('Is 10 a multiple of 3 and 5?', multiplesOfThreeAndFive(10))

gives the following results:

Image 18

Cartesian Product

Image 19

Let E and F be two sets. The cartesian product of E and F, denoted by E × F is the set of all ordered pairs (e, f) such that e is a member of E and f is a member of F.

Let CartesianProduct be the cartesian product operation. Thus, the CartesianProduct operation can be implemented as follows in TypeScript:

TypeScript
const cartesianProduct = <T1, T2>(e: Set<T1>, f: Set<T2>) => (x: T1, y: T2) => e(x) && f(y)

Running the code below:

TypeScript
console.log('\nCartesian Product:')
const cp = core.cartesianProduct(numbers.multipleOfThree, numbers.multipleOfFive)
console.log('Is (9, 15) in MultipleOfThree x MultipleOfFive? ', cp(9, 15))

gives the following results:

Image 20

Complements

Image 21

Let E and F be two sets. The relative complement of F in E, denoted by E \ F is the set of all elements which are members of E but not members of F.

Let Complement be the relative complement operation. Thus, the Complement operation can be implemented as follows in TypeScript:

TypeScript
const complement = <T>(e: Set<T>, f: Set<T>) => (x: T) => e(x) && !f(x)

Running the code below:

TypeScript
console.log('\nComplement:')
const c = core.complement(numbers.multipleOfThree, numbers.multipleOfFive)
console.log('Is 15 in MultipleOfThree \\ MultipleOfFive set? ', c(15))
console.log('Is 9 in MultipleOfThree \\ MultipleOfFive set? ', c(9))

gives the following results:

Image 22

Symmetric Difference

Image 23

Let E and F be two sets. The symmetric difference of E and F, denoted by E Δ F is the set of all elements which are members of either E and F but not in the intersection of E and F.

Let SymmetricDifference be the symmetric difference operation. Thus, the SymmetricDifference operation can be implemented in two ways in TypeScript. A trivial way is to use the union and complement operations as follows:

TypeScript
const symmetricDifferenceWithoutXor = <T>(e: Set<T>, f: Set<T>) => 
      (x: T) => union(complement<T>(e, f), complement(f, e))(x)

Another way is to use the XOR binary operation as follows:

TypeScript
const symmetricDifferenceWithXor = <T>(e: Set<T>, f: Set<T>) => (x: T) => e(x) !== f(x)

Running the code below:

TypeScript
console.log('\nSymmetricDifference without XOR:')
const sdWithoutXor = core.symmetricDifferenceWithoutXor(numbers.prime, numbers.even)
console.log('Is 2 in the symetric difference of prime and even Sets? ', sdWithoutXor(2))
console.log('Is 4 in the symetric difference of prime and even Sets? ', sdWithoutXor(4))
console.log('Is 7 in the symetric difference of prime and even Sets? ', sdWithoutXor(7))

console.log('\nSymmetricDifference with XOR:')
const sdWithXor = core.symmetricDifferenceWithXor(numbers.prime, numbers.even)
console.log('Is 2 in the symetric difference of prime and even Sets? ', sdWithXor(2))
console.log('Is 4 in the symetric difference of prime and even Sets? ', sdWithXor(4))
console.log('Is 7 in the symetric difference of prime and even Sets? ', sdWithXor(7))

gives the following results:

Image 24

Other Operations

This section presents other useful binary operations on sets.

Contains

Let Contains be the operation that checks whether or not an element is in a set. This operation is a function that takes as parameter an element and returns true if the element is in the set, false otherwise.

Thus, this operation is defined as follows in TypeScript:

TypeScript
const contains = <T>(e: Set<T>, x: T) => e(x)

Therefore, running the code below:

TypeScript
console.log('\nContains:')
console.log('Is 7 in the singleton {0}? ', core.contains(common.singleton(0), 7))
console.log('Is 7 in the singleton {7}? ', core.contains(common.singleton(7), 7))

gives the following result:

Image 25

Add

Let Add be the operation that adds an element to a set. This operation is a function that takes as parameter an element and adds it to the set.

Thus, this operation is defined as follows in TypeScript:

TypeScript
const add = <T>(e: Set<T>, y: T) => (x: T) => x === y || e(x)

Therefore, running the code below:

TypeScript
console.log('\nAdd:')
console.log('Is 7 in {0, 7}? ', core.add<number>(common.singleton(0), 7)(7))
console.log('Is 0 in {1, 0}? ', core.add<number>(common.singleton(1), 0)(0))
console.log('Is 7 in {19, 0}? ', core.add<number>(common.singleton(19), 0)(7))

gives the following result:

Image 26

Remove

Let Remove be the operation that removes an element from a set. This operations is a function that takes as parameter an element and removes it from the set.

Thus, this operation is defined as follows in TypeScript:

TypeScript
const remove = <T>(e: Set<T>, y: T) => (x: T) => x !== y && e(x)

Therefore, running the code below:

TypeScript
console.log('\nRemove:')
console.log('Is 7 in {}? ', core.remove<number>(common.singleton(0), 0)(7))
console.log('Is 0 in {}? ', core.remove<number>(common.singleton(7), 7)(0))

gives the following result:

Image 27

For Those Who Want To Go Further

You can see how easy we can do some algebra of sets in TypeScript through Functional Programming. In the previous sections was shown the most fundamental definitions. But, If you want to go further, you can think about:

  • Relations over sets
  • Abstract algebra, such as monoids, groups, fields, rings, K-vectorial spaces and so on
  • Inclusion-exclusion principle
  • Russell's paradox
  • Cantor's paradox
  • Dual vector space
  • Theorems and Corollaries

Euclidean Plane

In the previous section, the fundamental concepts on sets were implemented in TypeScript. In this section, we will practice the concepts implemented on the Euclidean plane.

Drawing a Disk

Image 28

A disk is a subset of a plane bounded by a circle. There are two types of disks. Closed disks which are disks that contain the points of the circle that constitutes its boundary, and Open disks which are disks that do not contain the points of the circle that constitutes its boundary.

In this section, we will set up the Characterstic function of the Closed disk and draw it in a HTML5 page.

To set up the Characterstic function, we first need a function that calculates the Euclidean Distance between two points in the plane. This function is implemented as follows:

TypeScript
function distance(p1: Point, p2: Point) {
    return Math.sqrt((p1.x - p2.x) ** 2 + (p1.y - p2.y) ** 2)
}

where Point is defined below:

TypeScript
class Point {
    x: number
    y: number

    constructor(x: number, y: number) {
        this.x = x
        this.y = y
    }
}

This formula is based on Pythagoras' Theorem.

Image 29

where c is the Euclidean distance, is (p1.X - p2.X)² and is (p1.Y - p2.Y)².

Let Disk be the Characteristic function of a closed disk. In algebra of sets, the definition of a closed disk in the reals set is as follows:

Image 30

where a and b are the coordinates of the center and R the radius.

Thus, the implementation of Disk in TypeScript is as follows:

TypeScript
const disk = (center: Point, radius: number) => (p: Point) => distance(p, center) <= radius

In order to view the set in a HTML5 page, I decided to implement a function draw that draws a set in the Euclidean plane. I chose HTML5 and thus used the canvas element for drawing.

Thus, I've built the Euclidean plane illustrated below through the method draw.

Image 31

Below the implementation of the plane.

TypeScript
class Plane {
  width: number
  height: number

  constructor(width: number, height: number) {
    this.width = width
    this.height = height
  }

  draw(set: PlaneSet, canvasId: string) {
    const canvas = document.getElementById(canvasId) as HTMLCanvasElement
    if (!canvas) throw new Error(`Canvas with id ${canvasId} not found`)
    canvas.width = this.width
    canvas.height = this.height
    const context = canvas.getContext('2d') as CanvasRenderingContext2D
    const semiWidth = this.width / 2
    const semiHeight = this.height / 2
    const xMin = -semiWidth
    const xMax = semiWidth
    const yMin = -semiHeight
    const yMax = semiHeight
    for (let x = 0; x < this.width; x++) {
      const xp = xMin + (x * (xMax - xMin)) / this.width
      for (let y = 0; y < this.height; y++) {
        const yp = yMax - (y * (yMax - yMin)) / this.height
        if (set(new Point(xp, yp))) context.fillRect(x, y, 1, 1)
      }
    }
  }

  clear(canvasId: string) {
    const canvas = document.getElementById(canvasId) as HTMLCanvasElement
    if (!canvas) throw new Error(`Canvas with id ${canvasId} not found`)
    const context = canvas.getContext('2d') as CanvasRenderingContext2D
    context.clearRect(0, 0, this.width, this.height)
  }
}

In the draw function, a canvas having the same width and the same height as the Euclidean plane container is created. Then each point in pixels (x,y) of the canvas is replaced by a black point if it belongs to the set. xMin, xMax, yMin and yMax are the bounding values illustrated in the figure of the Euclidean plane above.

Running the code below:

TypeScript
euclideanPlane = new Plane(200, 200)
euclideanPlane.draw(disk(new Point(0, 0), 50), 'disk')

where disk is the id of the canvas:

HTML
<canvas id="disk"></canvas>

gives the following result:

Image 32

Drawing Horizontal and Vertical Half-planes

Image 33

A horizontal or a vertical half-plane is either of the two subsets into which a plane divides the Euclidean space. A horizontal half-plane is either of the two subsets into which a plane divides the Euclidean space through a line perpendicular with the Y axis like in the figure above. A vertical half-plane is either of the two subsets into which a plane divides the Euclidean space through a line perpendicular with the X axis.

In this section, we will set up the Characteristic functions of the horizontal and vertical half-planes, draw them in a HTML5 page and see what we can do if we combine them with the disk subset.

Let HorizontalHalfPlane be the Characteristic function of a horizontal half-plane. The implementation of HorizontalHalfPlane in TypeScript is as follows:

TypeScript
const horizontalHalfPlane = (y: number, isLowerThan: boolean) => 
      (p: Point) => (isLowerThan ? p.y <= y : p.y >= y)

Thus, running the code below:

TypeScript
euclideanPlane.draw(horizontalHalfPlane(0, true),'hhp')

where hhp is the id of the canvas:

HTML
<canvas id="hhp"></canvas>

gives the following result:

Image 34

Let VerticalHalfPlane be the Characteristic function of a vertical half-plane. The implementation of VerticalHalfPlane in TypeScript is as follows:

TypeScript
const verticalHalfPlane = (x: number, isLowerThan: boolean) => 
      (p: Point) => (isLowerThan ? p.x <= x : p.x >= x)

Thus, running the code below:

TypeScript
euclideanPlane.draw(verticalHalfPlane(0, false),'vhp')

where vhd is the id of the canvas:

HTML
<canvas id="vhd"></canvas>

gives the following result:

Image 35

In the first section of the article, we set up basic binary operations on sets. Thus, by combining the intersection of a disk and a half-plane for example, we can draw the half-disk subset.

Therefore, running the sample below:

TypeScript
euclideanPlane.draw(set.intersection(disk(new Point(0, 0), 50), 
                    verticalHalfPlane(0, false)), 'hd')

where hd is the id of the canvas:

HTML
<canvas id="hd"></canvas>

gives the following result:

Image 36

Functions

This section presents functions on the sets in the Euclidean plane.

Translate

Image 37

Let translatePoint be the function that translates a point in the plane. In Euclidean geometry, translatePoint is a function that moves a given point a constant distance in a specified direction. Thus the implementation in TypeScript is as follows:

TypeScript
const translatePoint = (deltax: number, deltay: number) => 
                       (p: Point) => new Point(p.x + deltax, p.y + deltay)

where (deltax, deltay) is the constant vector of the translation.

Let translate be the function that translates a set in the plane. This function is simply implemented as follows in TypeScript:

TypeScript
const translate = (e: PlaneSet, deltax: number, deltay: number) => 
                  (p: Point) => e(translatePoint(-deltax, -deltay)(p))

translate takes as parameters deltax which is the delta distance in the first Euclidean dimension and deltay which is the delta distance in the second Euclidean dimension. If a point P (x, y) is translated in a set S, then its coordinates will change to (x', y') = (x, delatx, y, deltay). Thus, the point (x' - delatx, y' - deltay) will always belong to the set S. In set algebra, translate is called isomorph, in other words, the set of all translations forms the translation group T, which is isomorphic to the space itself. This explains the main logic of the function.

Thus, running the code below in our HTML5 page:

TypeScript
let translate_timer: ReturnType<typeof setInterval>
function translate_op() {
  let deltay = 0
  clearTimeout(scale_timer)
  clearTimeout(rotate_timer)
  translate_timer = setInterval(() => {
    deltay = deltay <= euclideanPlane.height ? deltay + 20 : 0
    euclideanPlane.draw(translate(disk(new Point(0, -50), 50), 0, deltay), 'ep_op')
  }, 1000)
}

where ep_op is the id of the canvas:

HTML
<canvas id="ep_op"></canvas>

gives the following result:

Image 38

Homothety

Image 39

Let scalePoint be the function that sends any point M to another point N such that the segment SN is on the same line as SM, but scaled by a factor λ. In algebra of sets, Scale is formulated as follows:

Image 40

Thus the implementation in TypeScript is as follows:

TypeScript
const scalePoint = (lambdax: number, lambday: number, deltax: number, deltay: number) 
      => (p: Point) => new Point(lambdax * p.x + deltax, lambday * p.y + deltay)

where (deltax, deltay) is the constant vector of the translation and (lambdax, lambday) is the lambda vector.

Let scale be the function that applies an homothety on a set in the plan. This function is simply implemented as follows in TypeScript:

TypeScript
const scale = (e: PlaneSet, lambdax: number, lambday: number, deltax: number, 
               deltay: number) => (p: Point) => e(scalePoint(1 / lambdax, 1 / lambday, 
               -deltax / lambdax, -deltay / lambday)(p))

scale takes as parameters deltax which is the delta distance in the first Euclidean dimension, deltay which is the delta distance in the second Euclidean dimension and (lambdax, lambday) which is the constant factor vector λ. If a point P (x, y) is transformed through scale in a set S, then its coordinates will change to (x', y') = (lambdax * x, delatx, lambday * y, deltay). Thus, the point ((x'- delatx)/lambdax, (y' - deltay)/lambday) will always belong to the set S, If lambda is different from the vector 0, of course. In algebra of sets, scale is called isomorph, in other words, the set of all homotheties forms the Homothety group H, which is isomorphic to the space itself \ {0}. This explains the main logic of the function.

Thus, running the code below in our HTML5 page:

TypeScript
let scale_timer: ReturnType<typeof setInterval>
function scale_op() {
  let deltay = 0
  let lambday = 0.05
  clearTimeout(translate_timer)
  clearTimeout(rotate_timer)
  scale_timer = setInterval(() => {
    deltay = deltay <= euclideanPlane.height ? deltay + 20 : 0
    lambday = deltay <= euclideanPlane.height ? lambday + 0.05 : 0.05
    euclideanPlane.draw(scale(disk(new Point(0, -50), 50), 1, lambday, 0, deltay), 'ep_op')
  }, 1000)
}

gives the following result:

Image 41

Rotate

Image 42

Let rotatePoint be the function that rotates a point with an angle θ. In matrix algebra, rotatePoint is formulated as follows:

Image 43

where (x', y') are the co-ordinates of the point after rotation, and the formula for x' and y' is as follows:

Image 44

The demonstration of this formula is very simple. Have a look at this rotation.

Image 45

Below the demonstration:

Image 46

Thus the implementation in TypeScript is as follows:

TypeScript
const rotatePoint = (theta: number) => (p: Point) => new Point(p.x * Math.cos(theta) 
      - p.y * Math.sin(theta), p.x * Math.sin(theta) + p.y * Math.cos(theta))

Let rotate be the function that applies a rotation on a set in the plane with the angle θ. This function is simply implemented as follows in TypeScript.

TypeScript
const rotate = (e: PlaneSet, theta: number) => (p: Point) => e(rotatePoint(-theta)(p))

rotate is a function that takes as parameter theta which is the angle of the rotation. If a point P (x, y) is transformed through rotate in a set S, then its coordinates will change to (x', y') = (x * cos(theta) - y * sin(theta), x * sin(theta), y * cos(theta)). Thus, the point (x' * cos(theta), y' * sin(theta), y' * cos(theta) - x' * sin(theta)) will always belong to the set S. In algebra of sets, rotate is called isomorph, in other words, the set of all rotations forms the Rotation group R, which is isomorphic to the space itself. This explains the main logic of the function.

Thus, running the code below in our HTML5 page:

TypeScript
let rotate_timer: ReturnType<typeof setInterval>
function rotate_op() {
  let theta = 0
  clearTimeout(translate_timer)
  clearTimeout(scale_timer)
  rotate_timer = setInterval(() => {
    euclideanPlane.draw(rotate(horizontalHalfPlane(-90, true), theta), 'ep_op')
    theta = (theta + Math.PI / 2) % (2 * Math.PI)
  }, 1000)
}

gives the following result:

Image 47

For Those Who Want to Go Further

Very simple, isn't it? For those who want to go further, you can explore these:

  • Ellipse
  • Three-dimensional Euclidean space
  • Ellipsoide
  • Paraboloid
  • Hyperboloid
  • Spherical harmonics
  • Superellipsoid
  • Haumea
  • Homoeoid
  • Focaloid

Fractals

Image 48

Fractals are sets that have a fractal dimension that usually exceeds their topological dimension and may fall between the integers. For example, the Mandelbrot set is a fractal defined by a family of complex quadratic polynomials:

Pc(z) = z^2 + c

where c is a complex. The Mandelbrot fractal is defined as the set of all points c such that the above sequence does not escape to infinity. In algebra of sets, this is formulated as follows:

Image 49

Fractals (abstract data type) can always be represented as follows in TypeScript:

TypeScript
type Fractal = (z: Complex, c: Complex) => Complex

Complex Numbers and Drawing

In order to be able to draw fractals, I needed to manipulate Complex numbers. Thus, I created the Complex class below:

TypeScript
class Complex {
    x: number
    y: number
    static zero = new Complex(0, 0)

    constructor(x: number, y: number) {
        this.x = x
        this.y = y
    }

    abs() {
        return Math.sqrt(this.x * this.x + this.y * this.y)
    }

    toString() {
        return this.x + ' + i * ' + this.y
    }
}

function add(z1: Complex, z2: Complex) {
    return new Complex(z1.x + z2.x, z1.y + z2.y)
}

function substract(z1: Complex, z2: Complex) {
    return new Complex(z1.x - z2.x, z1.y - z2.y)
}

function multiply(z1: Complex, z2: Complex) {
    return new Complex(z1.x * z2.x - z1.y * z2.y, z1.x * z2.y + z1.y * z2.x)
}

Mandelbrot Fractal

I created a Mandelbrot Fractal (abstract data type representation) P(z) = z^2 + c that is available below.

TypeScript
const mandelbrot = (z: Complex, c: Complex) => add(multiply(z, z), c)

In order to be able to draw Complex numbers, I created a ComplexPlane class. Below is the implementation in TypeScript.

TypeScript
class ComplexPlane {
  width: number
  height: number
  real_min: number
  real_max: number
  imaginary_min: number
  imaginary_max: number
  boundary: number
  fractalIterationsPerPixel: number
  canvasId: string

  constructor(
    width: number,
    height: number,
    real_min: number,
    real_max: number,
    imaginary_min: number,
    imaginary_max: number,
    boundary: number,
    fractalIterationsPerPixel: number,
    canvasId: string,
  ) {
    this.width = width
    this.height = height
    this.real_min = real_min
    this.real_max = real_max
    this.imaginary_min = imaginary_min
    this.imaginary_max = imaginary_max
    this.boundary = boundary
    this.fractalIterationsPerPixel = fractalIterationsPerPixel
    this.canvasId = canvasId
  }

  draw(fractal: Fractal) {
    const canvas = document.getElementById(this.canvasId) as HTMLCanvasElement
    canvas.width = this.width
    canvas.height = this.height
    const context = canvas.getContext('2d') as CanvasRenderingContext2D
    context.fillStyle = 'white'
    for (let x = 0; x < this.width; x++) {
      const xp = this.real_min + (x * (this.real_max - this.real_min)) / this.width
      for (let y = 0; y < this.height; y++) {
        const yp = this.imaginary_max - (y * (this.imaginary_max - this.imaginary_min)) / this.height
        const c = new Complex(xp, yp)
        let z = Complex.zero
        for (let k = 0; k < this.fractalIterationsPerPixel; k++) z = fractal(z, c)
        if (z.abs() < this.boundary) context.fillRect(x, y, 1, 1)
      }
    }
  }

  /*
   * Display 'Please wait...' at the center of the canvas
   *
  */
  pleaseWait() {
    const canvas = document.getElementById(this.canvasId) as HTMLCanvasElement
    canvas.width = this.width
    canvas.height = this.height
    const context = canvas.getContext('2d') as CanvasRenderingContext2D
    context.fillStyle = 'white'
    context.fillText('Please wait...', this.width / 2 - 30, this.height / 2)
  }
}

Thus, running the code below:

TypeScript
const complexPlane = new ComplexPlane(300, 300, -1.5, 1.5, -1.5, 1.5, 1.5, 20, 'fractal')

const mandelbrot = (z: Complex, c: Complex) => add(multiply(z, z), c)

complexPlane.pleaseWait()

setTimeout(() => complexPlane.draw(mandelbrot), 500)

where fractal is the id of the canvas:

HTML
<canvas id="fractal"></canvas>

gives the following result:

Image 50

For Those Who Want to Go Further

For those who want to go further, you can explore these:

  • Newton Fractals
  • Julia Fractals
  • Other Fractals

That's it! I hope you enjoyed reading.

History

  • 20th October, 2023:
    • Initial release
  • 27th October, 2023:
    • Added Babel transcompiler
    • Added eslint preset
    • Updated Complex class
    • Updated Fractal type
    • Updated plane drawing and animations
    • Updated fractals drawing
  • 11th April, 2024:
    • Bump @babel/cli from 7.23.4 to 7.24.1
    • Bump @babel/preset-env from 7.23.3 to 7.24.4
    • Bump @types/node from 20.10.0 to 20.12.7
    • Bump @typescript-eslint/eslint-plugin from 6.12.0 to 7.6.0
    • Bump @typescript-eslint/parser from 6.12.0 to 7.6.0
    • Bump eslint from 8.54.0 to 9.0.0
    • Bump eslint-plugin-import from 2.29.0 to 2.29.1
    • Bump npm-check-updates from 16.14.11 to 16.14.18
    • Bump typescript from 5.2.2 to 5.4.5

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Engineer
Morocco Morocco
I build innovative and scalable solutions for digital media. With several years of software engineering experience, I have a strong background in web, mobile and desktop development, as well as media asset management and digital asset management systems.

My strength lies in the development of innovative solutions and the ability to adapt them to different industries looking to streamline or automate their work process or data management.

I am passionate about learning new technologies and frameworks and applying them to solve complex and challenging problems. I am proficient in working with Node.js, React, React Native, TypeScript, C# and .NET among other languages and tools. My ultimate aim is to deliver high-quality software products that meet the requirements and expectations of our customers.

Open-source projects:

- Wexflow: .NET Workflow Engine and Automation Platform
- BookCars: Car Rental Platform with Mobile App
- Movin' In: Rental Property Management Platform with Mobile App
- Wexstream: Video Conferencing Platform
- wexCommerce: eCommerce Platform on Next.js

If you'd like to discuss any sort of opportunity, feel free to contact me through GitHub or LinkedIn.

Comments and Discussions

 
GeneralMy vote of 5 Pin
Rajesh Pillai22-May-24 17:28
Rajesh Pillai22-May-24 17:28 
GeneralMy vote of 5 Pin
Ștefan-Mihai MOGA21-Oct-23 3:15
professionalȘtefan-Mihai MOGA21-Oct-23 3:15 
GeneralMy vote of 5 Pin
RickZeeland20-Oct-23 1:47
mveRickZeeland20-Oct-23 1:47 

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