Chapter 8: Problem 4
Show that the diagonal elements of a skew-symmetric matrix are equal to \(0 .\)
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Chapter 8: Problem 4
Show that the diagonal elements of a skew-symmetric matrix are equal to \(0 .\)
These are the key concepts you need to understand to accurately answer the question.
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Let \(V\) be a finite dimensional vector space over the field \(K\), with a nondegenerate bilinear form \(\langle,\),\(rangle . If A: V \rightarrow V\) is a linear map such that $$ \langle A v, A w\rangle=\langle v, w\rangle $$ for all \(v, w \in V\), show that \(\operatorname{Det}(A)=\pm 1\).
Let \(A=\left(a_{i j}\right)\) be an \(m \times n\) real or complex matrix. Define a generalization of the absolute value, namely $$ |A|=m n \cdot \max \left|a_{i j}\right|. $$ (There will be no confusion with the determinant which does not occur in the present context.) If \(A, B\) are matrices which can be added, show that $$ |A+B| \leq|A|+|B|. $$ If they can be multiplied, show that $$ |A B| \leq|A||B| . $$ If \(c\) is a number, show that $$ |c A|=|c||A|. $$
(a) Let \(V\) be a finite dimensional space over \(\mathbf{R}\), with a positive definite sealar product, and let \(\left\\{v_{1}, \ldots, v_{n}\right\\}=\beta\) and \(\left\\{w_{1}, \ldots, w_{n}\right\\}=B^{\prime}\) be orthonormal bases of \(V\). Show that the matrix \(M_{\mathbb{G}^{\prime}}^{\mathbb{W}}(i d)\) is real unitary. [Hint: Use \(\left\langle w_{i}, w_{i}\right\rangle=1\) and \(\left\langle w_{i}, w_{j}\right\rangle=0\) if \(i \not A j\), as well as the expression \(w_{i}=\sum a_{i j} v_{j}\), for some \(\left.a_{i j} \in \mathbf{R} .\right]\). (b) Let \(F: V \rightarrow V\) be such that \(F\left(v_{i}\right)=w_{i}\) for all \(i\). Show that \(M_{\text {' }}^{B}(F)\) is unitary.
Show that the diagonal elements of a hermitian matrix are real.
Let \(V\) be a finite dimensional vector space over a field \(K .\) Let \(f: V \rightarrow K\) be a function, and assume that the funetion \(g\) such that $$ g(v, w)=f(v+w)-f(v)-f(w) $$ is bilinear. Assume that \(f(a v)=a^{2} f(v)\) for all \(v \in V\) and \(a \in K\). Show that \(f\) is a quadratic form, and determine a bilinear form from which it comes. Show that this bilinear form is unique.
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