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Are Inverse Matrices Orthogonal?

Published in Linear Algebra 2 mins read

No, inverse matrices are not necessarily orthogonal.

Understanding Inverse Matrices

An inverse matrix is a matrix that, when multiplied by the original matrix, results in the identity matrix. Think of it as the opposite of the original matrix.

Understanding Orthogonal Matrices

An orthogonal matrix is a square matrix whose inverse is equal to its transpose. This means that the columns (and rows) of an orthogonal matrix are orthonormal vectors, meaning they are perpendicular to each other and have a length of 1.

Key Differences

  • Inverse matrices don't have any specific restrictions on their columns or rows. They simply need to satisfy the inverse property.
  • Orthogonal matrices have strict requirements for their columns and rows, ensuring they are orthonormal.

Example

Let's consider the following matrix:

A = [[2, 1], [1, 2]]

The inverse of A is:

A⁻¹ = [[2/3, -1/3], [-1/3, 2/3]]

A⁻¹ is not equal to the transpose of A, so A is not orthogonal.

Conclusion

While inverse matrices are essential in linear algebra, they are not necessarily orthogonal. Orthogonality is a specific property that requires a matrix to have orthonormal columns and rows.

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