Tensor calculus - The properties of the Tensors

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We have a given a tensor $(2,0)$ and its components are, $M^{\alpha \beta} = \begin{pmatrix} 0 & 1 & 0 & 0 \\ 1 & -1 & 0 & 2 \\ 2 & 0 & 0 & 1 \\ 1 & 0 & -2 & 0 \end{pmatrix}$

The questions ask us to find the components of

(i) $M^{\alpha}_{\beta}$

(ii) $M^{\beta}_{\alpha}$

(iii) $M_{\alpha \beta}$

Answers

(i)

I used the $M^{\alpha}_{\beta} = \eta_{\beta \mu}M^{\alpha \mu}$ for $\eta_{\beta \mu} = diag(-1,1,1,1)$

If my calculations are corret I find $M^{\alpha}_{\beta} = \begin{pmatrix} 0 & -1 & -2 & -1 \\ 1 & -1 & 0 & 0 \\ 0 & 0 & 0 & -2 \\ 0 & -2 & -1 & 0 \end{pmatrix}$

(ii)

Similarly I thought I can write

$M^{\beta}_{\alpha} = \eta_{\alpha \mu}M^{\beta \mu}$

(iii)

$M_{\alpha \beta} = \eta_{\alpha \gamma}\eta_{\beta \mu}M^{\gamma \mu}$

These can be calculated by using algebra but my question is, can we take a shortcut ?

Questions

Q1) Can we say that the $M^{\beta}_{\alpha} = (M^{\alpha}_{\beta})^T$ ?

Q2) Can we say that $M_{\alpha \beta} M^{\alpha \beta} = I$ Where I is the identity matrix?

Q3) For a given $(m,n)$ tensor can we always say that, the components of the $(m,n)$ tensor times the components of the $(n,m)$ tensor gives an identity matrix (i.e $T^{\alpha \beta}_{\gamma}T^{\gamma} _{\alpha \beta} = I$)?

Q4) Similarly for a given $(n,n)$ matrix (i.e $T^{\beta \gamma}_{\alpha \mu}$) can we say that the transpose of the components will always gives the components of the $T^{\alpha \mu}_{\beta \gamma}$

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To answer your questions:

$1)$ No, since

$$M_\beta^\alpha = \begin{pmatrix} 0 & 1 & 0 & 0 \\ -1 & -1 & 0 & 2 \\ -2 & 0 & 0 & 1 \\ -1 & 0 & -2 & 0 \end{pmatrix}$$

$$M_\alpha^\beta = \begin{pmatrix} 0 & -1 & 0 & 0 \\ 1 & -1 & 0 & 2 \\ 2 & 0 & 0 & 1 \\ 1 & 0 & -2 & 0 \end{pmatrix}$$

These don't look like transposes to me.

$2)$ No, since the quantity you describe contracts all of the indices, there is no way it could be anything other than a scalar.

$3)$ No, for the same reason as $2$

$4)$ No, for the same reason as $1$