Zeriegen Sie die folgenden Matrizen in ihre Real- und Imaginärteile und prüfen Sie dann, welche Matrizen hermitesch bzw. schiefhermitesch sind: \(\mathbf{A}=\left(\begin{array}{cc}-\mathrm{j} & -5+2 \mathrm{j} \\ 5+2 \mathrm{j} & -4 \mathrm{j}\end{array}\right), \quad \mathbf{B}=\left(\begin{array}{cc}1 & 2-4 \mathrm{j} \\ 2+4 \mathrm{j} & 2\end{array}\right)\) \(C=\left(\begin{array}{rrr}-j & 0 & 0 \\ 0 & -j & 0 \\ 0 & 0 & -j\end{array}\right), \quad D=\left(\begin{array}{ccc}1 & -j & 1-2 j \\ j & 2 & 4 \\ 1+2 j & 4 & 3\end{array}\right)\) Welchen Wert besitzen die zugehôrigen Determinanten?

Short Answer

Expert verified
Matrix A is skew-Hermitian, C is both Hermitian and skew-Hermitian; B and D are neither. Determinants: A=-1, B=-16, C=-1, D=0.

Step by step solution

01

Write down the given matrices

Let the given matrices be as follows:\[ \mathbf{A}=\left(\begin{array}{cc}-\mathrm{j} & -5+2 \mathrm{j} \ 5+2 \mathrm{j} & -4 \mathrm{j}\end{array}\right), \quad \mathbf{B}=\left(\begin{array}{cc}1 & 2-4 \mathrm{j} \ 2+4 \mathrm{j} & 2\end{array}\right) \] \[ \mathbf{C}=\left(\begin{array}{rrr} -j & 0 & 0 \ 0 & -j & 0 \ 0 & 0 & -j \end{array}\right), \quad \mathbf{D}=\left(\begin{array}{ccc} 1 & -j & 1-2 j \ j & 2 & 4 \ 1+2 j & 4 & 3 \end{array}\right) \]
02

Find the real part of each matrix

The real part of a matrix is obtained by taking the real part of each element individually. For matrix \( \mathbf{A} \): \[ \text{Re}(\mathbf{A})=\left(\begin{array}{cc} 0 & -5 \ 5 & 0 \end{array}\right) \] For matrix \( \mathbf{B} \): \[ \text{Re}(\mathbf{B})=\left(\begin{array}{cc} 1 & 2 \ 2 & 2 \end{array}\right) \] For matrix \( \mathbf{C} \): \[ \text{Re}(\mathbf{C})=\left(\begin{array}{rrr} 0 & 0 & 0 \ 0 & 0 & 0 \ 0 & 0 & 0 \end{array}\right) \] For matrix \( \mathbf{D} \): \[ \text{Re}(\mathbf{D})=\left(\begin{array}{ccc} 1 & 0 & 1 \ 0 & 2 & 4 \ 1 & 4 & 3 \end{array}\right) \]
03

Find the imaginary part of each matrix

The imaginary part of a matrix is obtained by taking the coefficient of \( \mathrm{j} \) in each element. For matrix \( \mathbf{A} \): \[ \text{Im}(\mathbf{A})=\left(\begin{array}{cc} -1 & 2 \ 2 & -4 \end{array}\right) \] For matrix \( \mathbf{B} \): \[ \text{Im}(\mathbf{B})=\left(\begin{array}{cc} 0 & -4 \ 4 & 0 \end{array}\right) \] For matrix \( \mathbf{C} \): \[ \text{Im}(\mathbf{C})=\left(\begin{array}{rrr} -1 & 0 & 0 \ 0 & -1 & 0 \ 0 & 0 & -1 \end{array}\right) \] For matrix \( \mathbf{D} \): \[ \text{Im}(\mathbf{D})=\left(\begin{array}{ccc} 0 & -1 & -2 \ 1 & 0 & 0 \ 2 & 0 & 0 \end{array}\right) \]
04

Check if the matrices are Hermitian or skew-Hermitian

A matrix \( \mathbf{M} \) is Hermitian if \( \mathbf{M} = \mathbf{M}^{\dagger} \) and skew-Hermitian if \( \mathbf{M} = -\mathbf{M}^{\dagger} \), where \( \mathbf{M}^{\dagger} \) is the conjugate transpose of \( \mathbf{M} \). For matrix \( \mathbf{A} \), \( \mathbf{A}^{\dagger}eq \mathbf{A} \) and \( \mathbf{A}^{\dagger}=-\mathbf{A} \), so \( \mathbf{A} \) is skew-Hermitian. For matrix \( \mathbf{B} \), neither \( \mathbf{B}^{\dagger}=\mathbf{B} \) nor \( \mathbf{B}^{\dagger}=-\mathbf{B} \), so \( \mathbf{B} \) is neither Hermitian nor skew-Hermitian. For matrix \( \mathbf{C} \), \( \mathbf{C}^{\dagger}=\mathbf{C} \), so \( \mathbf{C} \) is Hermitian and \( \mathbf{C} \) is skew-Hermitian since \( \mathbf{C}^{\dagger}=-\mathbf{C} \). For matrix \( \mathbf{D} \), neither \( \mathbf{D}^{\dagger}=\mathbf{D} \) nor \( \mathbf{D}^{\dagger}=-\mathbf{D} \). so \( \mathbf{D} \) is neither Hermitian nor skew-Hermitian.
05

Calculate the determinants of the matrices

Determine the determinants of the matrices: For matrix \( \mathbf{A} \):\[ \text{det}(\mathbf{A})=(-\mathrm{j})(-4\mathrm{j}) - (-5+2\mathrm{j})(5+2\mathrm{j}) = -12 \] For matrix \( \mathbf{B} \):\[ \text{det}(\mathbf{B})=1(2) - (2-4\mathrm{j})(2+4\mathrm{j}) = -15 \] For matrix \( \mathbf{C} \):\[ \text{det}(\mathbf{C})=(-\mathrm{j})^3 = -\mathrm{j}^3 = 1 \] For matrix \( \mathbf{D} \):\[ \text{det}(\mathbf{D}) = 1* (2*3 - 4*4) - (-\mathrm{j}(24 - 4) + (1-2\mathrm{j})*4\mathrm{j} -50-10\mathrm{j} - 4 ) = 0 \]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Hermitian and Skew-Hermitian Matrices
Hermitian and skew-Hermitian matrices are types of complex matrices that play a fundamental role in many aspects of linear algebra and quantum mechanics. A Hermitian matrix is one that is equal to its own conjugate transpose, i.e., \(\textbf{M} = \textbf{M}^\text{†}\). In contrast, a skew-Hermitian matrix is one that equals the negative of its conjugate transpose, i.e., \(\textbf{M} = -\textbf{M}^\text{†}\). These matrices often possess real eigenvalues and are closely related to unitary matrices.
Matrix Decomposition
Matrix decomposition is a technique to break matrices into simpler, more manageable pieces. There are various forms of matrix decomposition such as LU decomposition, QR decomposition, and eigenvalue decomposition.
For complex matrices, decomposing into real and imaginary parts is particularly significant. Given a complex matrix \(\textbf{A}\), we can write it as \(\textbf{A} = \textbf{Re}(\textbf{A}) + j \textbf{Im}(\textbf{A})\), where \(\textbf{Re}(\textbf{A})\) is the real part and \(\textbf{Im}(\textbf{A})\) is the imaginary part.
Complex Matrices
Complex matrices are matrices where at least some of the elements are complex numbers. A complex number has both a real part and an imaginary part, usually expressed as \(a + bj\), where \(a\) and \(b\) are real numbers, and \(j\) is the imaginary unit satisfying \(j^2 = -1\).
In mathematical operations, complex matrices follow the same rules as real matrices, but with additional considerations for complex conjugation and imaginary units.
Real and Imaginary Parts
Every complex matrix has a real part and an imaginary part. The real part of a complex matrix is obtained by taking the real parts of each of its individual elements. Similarly, the imaginary part is obtained by taking the imaginary parts of each element.
For instance, given \(\textbf{A} = \begin{pmatrix} -j & -5+2j \ 5+2j & -4j \end{pmatrix}\), the real part is \(\textbf{Re}(\textbf{A}) = \begin{pmatrix} 0 & -5 \ 5 & 0 \end{pmatrix}\) and the imaginary part is \(\textbf{Im}(\textbf{A}) = \begin{pmatrix} -1 & 2 \ 2 & -4 \end{pmatrix}\).
Determinants and Conjugate Transpose
The determinant of a matrix provides important information about the matrix such as whether it is invertible. The determinant is a scalar value often calculated using cross-multiplication for 2x2 matrices or more advanced methods for larger matrices. Determinants for complex matrices are computed similarly, incorporating real and imaginary parts.
The conjugate transpose (\textbf{M}^\text{†}) is achieved by taking the transpose of the matrix (flipping rows and columns) and then taking the complex conjugate of each element. For example, given a matrix \(\textbf{A} = \begin{pmatrix} -j & -5+2j \ 5+2j & -4j \end{pmatrix}\), the conjugate transpose is \(\begin{pmatrix} j & 5-2j \ 5-2j & 4j \end{pmatrix}\). This operation is crucial in defining Hermitian and skew-Hermitian matrices.

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Most popular questions from this chapter

Matrix A beschreibt die Spiegelung eines Raumpunktes an der \(x, y\)-Ebene, Matrix B die Drehung des r?umlichen Koordinatensystems um die \(z\)-Achse um den Winkel \alpha. Zeigen Sic, daB beide Matrizen orthogonal sind. $$ \mathbf{A}=\left(\begin{array}{lll} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & -1 \end{array}\right), \quad B=\left(\begin{array}{ccc} \cos \alpha & \sin \alpha & 0 \\ -\sin \alpha & \cos \alpha & 0 \\ 0 & 0 & 1 \end{array}\right) $$

F?hren Sie mit den Matrizen $$ \mathbf{A}=\left(\begin{array}{rrr} 3 & 4 & 0 \\ -1 & 5 & 3 \end{array}\right), \quad B=\left(\begin{array}{rr} -3 & 3 \\ 1 & -1 \\ 0 & 2 \end{array}\right) \text { und } \quad \mathbf{C}=\left(\begin{array}{lll} 1 & 4 & 0 \\ 2 & 1 & 3 \end{array}\right) $$ die folgenden Rechenoperationen durch (soweit dies überhaupt m?glich ist): a) \(2 \mathrm{~A}+\mathbf{C}-\mathbf{B}^{\mathbf{T}}\) b) \(\quad \mathbf{A}^{\mathbf{T}}-\mathbf{B}-3 \boldsymbol{C}^{\mathbf{T}}\) c) \(\quad \mathbf{A}-2 \mathbf{C}+\mathbf{B}\)

Führen Sie die folgenden Determinanten h?herer Ordnung durch fortlaufende Reduzierung auf eine einzige 3-reihige Determinante zurück und berechnen Sie diese nach der Regel von Sarrus: a) \(\quad \operatorname{det} A=\left|\begin{array}{rrrr}-1 & -3 & 1 & 6 \\ 3 & 1 & 4 & 5 \\ -2 & -2 & 3 & 3 \\ -2 & -3 & 1 & 4\end{array}\right|\) b) \(\operatorname{det} \mathbf{A}=\left|\begin{array}{rrrrr}1 & 4 & 0 & 0 & 1 \\\ 2 & 0 & 1 & 2 & -1 \\ 1 & 1 & -2 & -3 & -4 \\ 3 & 4 & 0 & 0 & 1 \\ 0 & 1 & 1 & 3 & 5\end{array}\right|\)

Berechnen Sie unter Verwendung des Falk-Schemas die Matrizenprodukte \(\mathbf{A} \cdot \mathbf{A}=\mathbf{A}^{2}, \mathbf{A} \cdot \mathbf{B}, \mathbf{B} \cdot \mathbf{A}\) und \(\mathbf{B} \cdot \mathbf{B}=\mathbf{B}^{2}\) (soweit diese überhaupt existieren) für a) \(\quad \mathbf{A}=\left(\begin{array}{cc}2+j & 1+j \\ 2 & 1-j\end{array}\right)\). \(\quad\) B \(=\left(\begin{array}{ll}2 j & 3-3 j \\ 5 j & 1+2 j\end{array}\right)\) b) \(\quad \mathbf{A}=\left(\begin{array}{ccc}2 & 1+j & 1 \\ 1 & 5 & j\end{array}\right), \quad B=\left(\begin{array}{cc}1 & 1+2 j \\ 1-j & j \\\ 2 & 1-2 j\end{array}\right)\)

Die nachfolgenden Matrizen sind regulär. Berechnen Sie die jeweils zugehörige inverse Matrix nach dem Gau\beta-Jordan-Verfahren. $$ \mathbf{A}=\left(\begin{array}{rrr} 3 & 1 & 4 \\ 1 & 2 & 0 \\ 0 & 1 & -2 \end{array}\right), \quad \mathbf{B}=\left(\begin{array}{rrr} 4 & 5 & -1 \\ 2 & 0 & 1 \\ 3 & 1 & 0 \end{array}\right), \quad \mathbf{C}=\left(\begin{array}{lll} 3 & 4 & 2 \\ 1 & 5 & 3 \\ 0 & 1 & 0 \end{array}\right) $$

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