\(T(1,1)=(1,1)\), whose coordinates in \(B\) are \((1,0)\); \(T(1,-1)=(-1,1)=-(1,-1)\), with coordinates \((0,-1)\). These are the columns of the diagonal matrix \(\operatorname{diag}(1,-1)\). The standard matrix is \(\begin{pmatrix}0&1\\1&0\end{pmatrix}\).
The matrix \([T]\) of a linear transformation \(T\), with respect to given bases, has as columns the images of the domain basis vectors, written in coordinates of the codomain basis.
\[[T(v)]=[T]\,[v]\]
More practice problems: matrix of a linear transformation