# Complex Numbers #

Math.js supports the creation, manipulation, and calculations with complex numbers. Support of complex numbers is powered by the library complex.js.

In mathematics, a complex number is an expression of the form `a + bi`

,
where `a`

and `b`

are real numbers and `i`

represents the imaginary number
defined as `i^2 = -1`

. (In other words, `i`

is the square root of `-1`

.)
The real number `a`

is called the real part of the complex number,
and the real number `b`

is the imaginary part. For example, `3 + 2i`

is a
complex number, having real part `3`

and imaginary part `2`

.
Complex numbers are often used in applied mathematics, control theory,
signal analysis, fluid dynamics and other fields.

## Usage #

A complex number is created using the function `math.complex`

. This function
accepts:

- two numbers representing the real and imaginary part of the value,
- a single string containing a complex value in the form
`a + bi`

where`a`

and`b`

respectively represent the real and imaginary part of the complex number. - an object with either properties
`re`

and`im`

for the real and imaginary part of the value, or two properties`r`

and`phi`

containing the polar coordinates of a complex value. The function returns a`Complex`

object.

Syntax:

```
math.complex(re: number) : Complex
math.complex(re: number, im: number) : Complex
math.complex(complex: Complex) : Complex
math.complex({re: Number, im: Number}) : Complex
math.complex({r: number, phi: number}) : Complex
math.complex({abs: number, arg: number}) : Complex
math.complex(str: string) : Complex
```

Examples:

```
const a = math.complex(2, 3) // Complex 2 + 3i
a.re // Number 2
a.im // Number 3
const b = math.complex('4 - 2i') // Complex 4 - 2i
b.re = 5 // Number 5
b // Complex 5 - 2i
```

## Calculations #

Most functions of math.js support complex numbers. Complex and real numbers can be used together.

```
const a = math.complex(2, 3) // Complex 2 + 3i
const b = math.complex('4 - 2i') // Complex 4 - 2i
math.re(a) // Number 2
math.im(a) // Number 3
math.conj(a) // Complex 2 - 3i
math.add(a, b) // Complex 6 + i
math.multiply(a, 2) // Complex 4 + 6i
math.sqrt(-4) // Complex 2i
```

## API #

A `Complex`

object created by `math.complex`

contains the following properties and functions:

### complex.re #

A number containing the real part of the complex number. Can be read and replaced.

### complex.im #

A number containing the imaginary part of the complex number. Can be read and replaced.

### complex.clone() #

Create a clone of the complex number.

### complex.equals(other) #

Test whether a complex number equals another complex value.

Two complex numbers are equal when both their real and imaginary parts are equal.

### complex.neg() #

Returns a complex number with a real part and an imaginary part equal in magnitude but opposite in sign to the current complex number.

### complex.conjugate() #

Returns a complex number with an equal real part and an imaginary part equal in magnitude but opposite in sign to the current complex number.

### complex.inverse() #

Returns a complex number that is inverse of the current complex number.

### complex.toVector() #

Get the vector representation of the current complex number. Returns an array of size 2.

### complex.toJSON() #

Returns a JSON representation of the complex number, with signature
`{mathjs: 'Complex', re: number, im: number}`

.
Used when serializing a complex number, see Serialization.

### complex.toPolar() #

Get the polar coordinates of the complex number, returns
an object with properties `r`

and `phi`

.

### complex.toString() #

Returns a string representation of the complex number, formatted
as `a + bi`

where `a`

is the real part and `b`

the imaginary part.

### complex.format([precision: number]) #

Get a string representation of the complex number,
formatted as `a + bi`

where `a`

is the real part and `b`

the imaginary part.
If precision is defined, the units value will be rounded to the provided
number of digits.

## Static methods #

The following static methods can be accessed using `math.Complex`

### Complex.fromJSON(json) #

Revive a complex number from a JSON object. Accepts
An object `{mathjs: 'Complex', re: number, im: number}`

, where the property
`mathjs`

is optional.
Used when deserializing a complex number, see Serialization.

### Complex.fromPolar(r: number, phi: number) #

Create a complex number from polar coordinates.

### Complex.compare(a: Complex, b: Complex) #

Returns the comparision result of two complex number:

- Returns 1 when the real part of
`a`

is larger than the real part of`b`

- Returns -1 when the real part of
`a`

is smaller than the real part of`b`

- Returns 1 when the real parts are equal
and the imaginary part of
`a`

is larger than the imaginary part of`b`

- Returns -1 when the real parts are equal
and the imaginary part of
`a`

is smaller than the imaginary part of`b`

- Returns 0 when both real and imaginary parts are equal.

Example:

```
const a = math.complex(2, 3) // Complex 2 + 3i
const b = math.complex(2, 1) // Complex 2 + 1i
math.Complex.compare(a,b) // returns 1
//create from json
const c = math.Complex.fromJSON({mathjs: 'Complex', re: 4, im: 3}) // Complex 4 + 3i
```