Conjugate transpose

Conjugate transpose is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Suppose that a matrix $M$ contains complex numbers. Then the conjugate transpose of $M$ is a matrix $M^{H}$ containing the complex conjugates of the matrix transposition of $M$.

$(M^{H})_{ji}={\overline {M_{ij}}}$

This means that row $j$, column $i$ of the conjugate transpose equals the complex conjugate of row $i$, column $j$ of the original matrix.

In the next list, $M$ must also be a square matrix.

• A Hermitian matrix equals its own conjugate transpose: $M^{H}=M$.
• A normal matrix is commutative in multiplication with its conjugate transpose: $M^{H}M=MM^{H}$.
• A unitary matrix has its inverse equal to its conjugate transpose: $M^{H}=M^{-1}$. This is true iff $M^{H}M=I_{n}$ and iff $MM^{H}=I_{n}$, where $I_{n}$ is the identity matrix.

Given some matrix of complex numbers, find its conjugate transpose. Also determine if it is a Hermitian matrix, normal matrix, or a unitary matrix.

• MathWorld: conjugate transpose, Hermitian matrix, normal matrix, unitary matrix

Ruby

This example is incorrect. Please fix the code and remove this message. Details: Matrix#hermitian? in MRI uses a different definition of Hermitian matrix: it only checks $M_{ji}={\overline {M_{ij}}}$ for $i\neq j$.

Works with: Ruby version 1.9.3

<lang ruby>require 'matrix'

1. Start with some matrix.

i = Complex::I matrix = Matrix[[i, 0, 0],

               [0, i, 0],
               [0, 0, i]]

1. Find the conjugate transpose.
2. Matrix#conjugate appeared in Ruby 1.9.2.

conjt = matrix.conj.t # aliases for matrix.conjugate.tranpose print 'conjugate tranpose: '; puts conjt

if matrix.square?

 # These predicates appeared in Ruby 1.9.3.
 print 'Hermitian? '; puts matrix.hermitian?
 print '   normal? '; puts matrix.normal?
 print '  unitary? '; puts matrix.unitary?

else

 # Matrix is not square. These predicates would
 # raise ExceptionForMatrix::ErrDimensionMismatch.
 print 'Hermitian? false'
 print '   normal? false'
 print '  unitary? false'

end</lang>