# eye

Identity matrix

## Syntax

``I = eye``
``I = eye(n)``
``I = eye(n,m)``
``I = eye(sz)``
``I = eye(___,typename)``
``I = eye(___,'like',p)``

## Description

``I = eye` returns the scalar `1`.`

example

````I = eye(n)` returns an `n`-by-`n` identity matrix with ones on the main diagonal and zeros elsewhere.```

example

````I = eye(n,m)` returns an `n`-by-`m` matrix with ones on the main diagonal and zeros elsewhere.```

example

````I = eye(sz)` returns an array with ones on the main diagonal and zeros elsewhere. The size vector, `sz`, defines `size(I)`. For example, `eye([2,3])` returns a 2-by-3 array with ones on the main diagonal and zeros elsewhere.```

example

````I = eye(___,typename)` also specifies the data type (class) of `I` for any of the previous syntaxes. For example, `eye(5,'int8')` returns a 5-by-5 identity matrix consisting of 8-bit integers.```

example

````I = eye(___,'like',p)` specifies that `I` has the same data type, sparsity, and complexity (real or complex) as the numeric variable `p`.```

## Examples

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Create a 4-by-4 identity matrix.

`I = eye(4)`
```I = 4×4 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 ```

Create a 2-by-3 identity matrix.

`I = eye(2,3)`
```I = 2×3 1 0 0 0 1 0 ```

Create a 3-by-1 identity vector.

```sz = [3,1]; I = eye(sz)```
```I = 3×1 1 0 0 ```

Create a 3-by-3 identity matrix whose elements are 32-bit unsigned integers.

`I = eye(3,'uint32'),`
```I = 3x3 uint32 matrix 1 0 0 0 1 0 0 0 1 ```
`class(I)`
```ans = 'uint32' ```

Create a 2-by-2 identity matrix that is not real valued, but instead is complex like an existing array.

Define a complex vector.

`p = [1+2i 3i];`

Create an identity matrix that is complex like `p`.

`I = eye(2,'like',p)`
```I = 2×2 complex 1.0000 + 0.0000i 0.0000 + 0.0000i 0.0000 + 0.0000i 1.0000 + 0.0000i ```

Define a 5-by-5 sparse matrix.

`p = sparse(5,5,pi);`

Create a 5-by-5 identity matrix that is sparse like `P`.

`I = eye(5,'like',p)`
```I = (1,1) 1 (2,2) 1 (3,3) 1 (4,4) 1 (5,5) 1 ```

Define a 2-by-2 matrix of single precision.

`p = single([1 3 ; 2 4]);`

Create an identity matrix that is the same size and data type as `P`.

`I = eye(size(p),'like',p),`
```I = 2x2 single matrix 1 0 0 1 ```
`class(I)`
```ans = 'single' ```

## Input Arguments

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Size of first dimension of `I`, specified as an integer value.

• If `n` is the only integer input argument, then `I` is a square n-by-n identity matrix.

• If `n` is `0`, then `I` is an empty matrix.

• If `n` is negative, then it is treated as `0`.

Data Types: `double` | `single` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64`

Size of second dimension of `I`, specified as an integer value.

• If `m` is `0`, then `I` is an empty matrix.

• If `m` is negative, then it is treated as `0`.

Data Types: `double` | `single` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64`

Size of `I`, specified as a row vector of no more than two integer values.

• If an element of `sz` is `0`, then `I` is an empty matrix.

• If an element of `sz` is negative, then the element is treated as `0`.

Example: `sz = [2 3]` defines `I` as a 2-by-3 matrix.

Data Types: `double` | `single` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64`

Output class, specified as `'double'`, `'single'`, `logical`, `'int8'`, `'uint8'`, `'int16'`, `'uint16'`, `'int32'`, `'uint32'`, `'int64'`, or `'uint64'`.

Prototype, specified as a numeric variable.

Data Types: `double` | `single` | `logical` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64`
Complex Number Support: Yes