§
Cofactor as derivative of determinant
I saw this at
math.se
,
that one can define the cofactor of index
A
[
i
]
[
j
]
A[i][j]
A
[
i
]
[
j
]
of a matrix
A
A
A
as
∂
A
∂
A
[
i
]
[
j
]
\frac{\partial A}{\partial A[i][j]}
∂
A
[
i
]
[
j
]
∂
A
which I think is quite cool.