Section IX.1

§ 1

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Problem IX.1.1

Let B\mathcal{B} be the linear space of bilinear functions defined on an nn-dimensional linear space L\mathcal{L}, and let A\mathrm{A} be a linear transformation of the space B\mathcal{B}. Prove that A\mathrm{A} is a tensor of type (2,2)(2,2) in the space L\mathcal{L}.

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Problem IX.1.2
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(a)

How many components does a tensor of valence three have in a four-dimensional space?

(b)

How many terms does the expression of any one of its components in a new basis through the components in the old basis contain?

Problem IX.1.3

A tensor of type (0,n)(0, n) in an nn-dimensional linear space has in a basis e\mathbf{e} the components εi1…in=0\varepsilon_{i_{1} \ldots i_{n}}=0, if among the values i1,…,ini_{1}, \ldots , i_{n} there are equal ones, and

εi1…in=(−1)N(i1,…,in) \varepsilon _{i_{1} \ldots i_{n}}=(-1)^{N\left(i_{1}, \ldots , i_{n}\right)}

otherwise. Find the components of this tensor in the basis e′=eS\mathbf{e}^{\prime }=\mathbf{e} S.

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Problem IX.1.4

A linear function f\mathrm{f} is given in a basis e\mathbf{e} by a row f\mathbf{f}, and a vector aa by a column a\mathbf{a}. Find the matrix of the tensor a⊗fa \otimes \mathrm{f}. What geometric meaning does this tensor have?

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Problem IX.1.5

How many different tensors can be formed by means of contraction from a tensor of type (2,2)(2,2) ?

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Problem IX.1.6

Prove that the tensor from problem 3 is antisymmetric in any subset of the set of indices.

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Problem IX.1.7

Prove that for any tensor of type (1,1)(1,1) the equalities

aj(ialk)=a(jial)k,aj[ialk]=a[jial]k. a_{j}^{(i} a_{l}^{k)}=a_{(j}^{i} a_{l)}^{k}, \quad a_{j}^{[i} a_{l}^{k]}=a_{[j}^{i} a_{l]}^{k} .

hold.

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