# Orthogonal Matrix

An Orthogonal Matrix is a real square matrix whose columns and rows are orthogonal vectors.

**Context:**- It can range from being an Orthonormal Matrix to being a Non-Normalized Orthogonal Matrix.
- …
- It is used in matrix decomposition processes like QR Decomposition, Singular Value Decomposition, Eigen Decomposition, Polar Decomposition, etc.

**Example(s):**- an Identity Matrix.
- a Rotation Matrix.
- [math]\displaystyle{ \begin{bmatrix}x & 0 & 0\\ 0 & y & 0 \\0 & 0 & z\end{bmatrix} }[/math].
- [math]\displaystyle{ \begin{bmatrix}1 & 3 \\ 2 & 4 \end{bmatrix} }[/math], along with its normalized version [math]\displaystyle{ \begin{bmatrix}\frac{1}{\sqrt{5}} & \frac{2}{\sqrt{5}} \\ \frac{2}{\sqrt{5}} & -\frac{1}{\sqrt{5}} \end{bmatrix} }[/math].
- an x-Axis Reflection Matrix.
- a Coordinate Axes Permutation Matrix.
- …

**Counter-Example(s):****See:**Unitary Matrix, Orthogonal Transformation, Unit Vector, Orthonormality, Invertible Matrix, Normal Matrix.

## References

### 2015

- (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/orthogonal_matrix Retrieved:2015-2-16.
- In linear algebra, an
**orthogonal matrix**is a square matrix with real entries whose columns and rows are orthogonal unit vectors (i.e., orthonormal vectors), i.e. :[math]\displaystyle{ Q^\mathrm{T} Q = Q Q^\mathrm{T} = I, }[/math]where

*I*is the identity matrix.This leads to the equivalent characterization: a matrix

*Q*is orthogonal if its transpose is equal to its inverse: :[math]\displaystyle{ Q^\mathrm{T}=Q^{-1}, \, }[/math]An orthogonal matrix

*Q*is necessarily invertible (with inverse ), unitary () and therefore normal () in the reals. The determinant of any orthogonal matrix is either +1 or −1. As a linear transformation, an orthogonal matrix preserves the dot product of vectors, and therefore acts as an isometry of Euclidean space, such as a rotation or reflection. In other words, it is a unitary transformation.The set of

*n*×*n*orthogonal matrices forms a group O*(*n*), known as the orthogonal group. The subgroup*SO*(*n*) consisting of orthogonal matrices with determinant +1 is called the special orthogonal group, and each of its elements is a**special orthogonal matrix. As a linear transformation, every special orthogonal matrix acts as a rotation.**The complex analogue of an orthogonal matrix is a unitary matrix.*

- In linear algebra, an