Let $T:\mathbb{R}^2 \rightarrow \mathbb{R}^2$ with
$$T(x,y) = \left[ \begin{array}{ccc}
1x+2y \\
3x+4y \end{array} \right] $$
The matrix representation of $T$ is
$$ A= \left[ \begin{array}{ccc}
1 & 2 \\
3 & 4
\end{array} \right].$$
Now the adjoint of the operator $T$ is the transpose of $A$
$$ \left[ \begin{array}{ccc}
1 & 3 \\
2 & 4
\end{array} \right],$$
"Adjoints of operators generalize (conjugate) transposes of square
matrices."
On the other hand, the adjoint of the matrix $A$ is
$$\left[ \begin{array}{ccc}
4 & -2 \\
-3 & 1
\end{array} \right].$$
Is there any connection between the two? or the two "adjoint" definitions used here are unrelated.
Thanks!
Best Answer
I believe you are mistaken. The adjoint of the matrix A is the transpose of the matrix A.
One major confusion here is that there are two definitions for the word adjoint. The adjoint of a matrix is its conjugate transpose. Another definition, now often called the "classical adjoint" of a matrix is the matrix of its cofactors, which is what I think you write as the adjoint of the matrix A. Another now more common name for the classical adjoint of a matrix is its adjugate.