Derivative of $A^\top A$ Let $f(A):= A^\top A$ where $A$ is an $m \times n$ matrix.  We want to
find the derivative of $f$ with respect to $A$. By derivative we mean
to find the Jacobian of all partial derivatives of $f(A)$ with respect
to $A$. Here is how I proceed.
The Derivative of $f$ is the linear map $D f(A): X \to A^\top X +
X^\top A$. Let $K$ be the commutation matrix such that
$K\operatorname{vec}(X^\top A) = \operatorname{vec}(A^\top X)$.
Then,
\begin{align}
  \operatorname{vec}(A^\top X + X^\top A)
  & = \operatorname{vec}(A^\top X) + \operatorname{vec}(X^\top A) \\
  & = (I_n\otimes A^\top) \operatorname{vec}(X) +
    \operatorname{vec}(X^\top A) \\
  & = I_n (\otimes A^\top) \operatorname{vec}(X) +
    K_{n,n} \operatorname{vec}(A^\top X) \\
  & = (I_n \otimes A^\top) \operatorname{vec}(X) +
    K_{n, n} (I_n \otimes A^\top) \operatorname{vec}(X)
\end{align}
It now follows that
\begin{align}
  \frac{\partial f}{\partial A} & =  (I_n \otimes A^\top)
                                  + K_{n, n} (I_n \otimes A^\top)
\end{align}
In here I am using the fact that $\operatorname{vec}(AXB) = (B^\top \otimes A)\operatorname{vec}(X)$ where $\operatorname{vec}$ is the vectorization operator.
I was inspired by this answer and the corresponding equation under the section Differentials of Quadratic Products on this webpage
My Questions:


*

*Is this approach correct?. If not how do I go about finding the desired derivative?

*Where can I find references regarding this type of manipulation?. (I don't mean this particular manipulation, but a reference for derivatives of matrices in general). I looked on Horn and Johnson Matrix Analysis, but a 'commutation matrix' is nowhere to be found. When I say reference, I mean a rigorous linear algebraic exposition.
 A: Take the differential of the expression
$$\eqalign{
 F &= A^TA \cr
dF &= dA^T\,A + A^T\,dA \cr
}$$
At this point, you can either use vectorizations
$$\eqalign{
{\rm vec}(dF) &= {\rm vec}(dA^T\,A) + {\rm vec}(A^T\,dA) \cr
df &= (A^T\otimes I)(K\,da) + (I\otimes A^T)\,da \cr
\frac{\partial f}{\partial a} &= (A^T\otimes I)K + (I\otimes A^T) \cr
}$$
or tensor methods
$$\eqalign{
dF &= (I{\mathcal E}A^T):({\mathcal K}:dA) + (A^T{\mathcal E}I):dA \cr
\frac{\partial F}{\partial A}
 &= ({\mathcal E}A^T):{\mathcal K} + A^T{\mathcal E} \cr
}$$
where a colon represents the double-contraction product, i.e.
$$(X:{\mathcal E})_{kl} = \sum_{ij} X_{ij} {\mathcal E}_{ijkl} $$
while juxtapositions represent single-contractions
$$(X{\mathcal E}Y)_{ikmr} = \sum_{jp} X_{ij} {\mathcal E}_{jkmp} Y_{pr} $$
The isotropic 4th order tensors have components
$$\eqalign{
{\mathcal E}_{ijkl} &= \delta_{ik} \delta_{jl} \cr
{\mathcal K}_{ijkl} &= \delta_{il} \delta_{jk} \cr\cr
}$$
For references, try
"Matrix Differential Calculus" by Magnus and Neudecker
"Complex-Valued Matrix Derivatives" by Are Hjorungnes
A: You are close.  By my calculation (checked on a $2\,x\,2$ example)
$$\frac{\partial }{{\partial \underline {\overline {\bf{A}} } }}\left( {{{\underline {\overline {\bf{A}} } }^T}\underline {\overline {\bf{A}} } } \right) = \left( {{{\underline {\overline {\bf{I}} } }_{\left[ n \right]}} \otimes {{\underline {\overline {\bf{A}} } }^T}} \right) + \left( {{{\underline {\overline {\bf{A}} } }^T} \otimes {{\underline {\overline {\bf{I}} } }_{\left[ n \right]}}} \right){\underline {\overline {\bf{K}} } _{\left[ {m,n} \right]}}$$
Derivation:
$$\frac{\partial }{{\partial \underline {\overline {\bf{A}} } }}\left( {{{\underline {\overline {\bf{A}} } }^T}\underline {\overline {\bf{A}} } } \right) = {\left. {\frac{\partial }{{\partial \underline {\overline {\bf{A}} } }}\left( {{{\underline {\overline {\bf{A}} } }^T}\underline {\overline {\bf{A}} } } \right)} \right|_{{{\underline {\overline {\bf{A}} } }^T}{\rm{ constant}}}} + {\left. {\frac{\partial }{{\partial \underline {\overline {\bf{A}} } }}\left( {{{\underline {\overline {\bf{A}} } }^T}\underline {\overline {\bf{A}} } } \right)} \right|_{\underline {\overline {\bf{A}} } {\rm{ constant}}}}$$
For the first term
$${\underline {\overline {\bf{A}} } ^T}\underline {\overline {\bf{A}} }  = {\underline {\overline {\bf{A}} } ^T}\underline {\overline {\bf{A}} } \,{\underline {\overline {\bf{I}} } _{\left[ n \right]}} = \left( {{{\underline {\overline {\bf{I}} } }_{\left[ n \right]}} \otimes {{\underline {\overline {\bf{A}} } }^T}} \right){\rm{vec}}\left( {\underline {\overline {\bf{A}} } } \right)$$
so that
$${\left. {\frac{\partial }{{\partial \underline {\overline {\bf{A}} } }}\left( {{{\underline {\overline {\bf{A}} } }^T}\underline {\overline {\bf{A}} } } \right)} \right|_{{{\underline {\overline {\bf{A}} } }^T}{\rm{ constant}}}} = \left( {{{\underline {\overline {\bf{I}} } }_{\left[ n \right]}} \otimes {{\underline {\overline {\bf{A}} } }^T}} \right)$$
For the second term
$${\underline {\overline {\bf{A}} } ^T}\underline {\overline {\bf{A}} }  = {\underline {\overline {\bf{I}} } _{\left[ n \right]}}{\underline {\overline {\bf{A}} } ^T}\underline {\overline {\bf{A}} }  = \left( {{{\underline {\overline {\bf{A}} } }^T} \otimes {{\underline {\overline {\bf{I}} } }_{\left[ n \right]}}} \right){\rm{vec}}\left( {{{\underline {\overline {\bf{A}} } }^T}} \right) = \left( {{{\underline {\overline {\bf{A}} } }^T} \otimes {{\underline {\overline {\bf{I}} } }_{\left[ n \right]}}} \right){\underline {\overline {\bf{K}} } _{\left[ {m,n} \right]}}{\rm{vec}}\left( {\underline {\overline {\bf{A}} } } \right)$$
so that
$${\left. {\frac{\partial }{{\partial \underline {\overline {\bf{A}} } }}\left( {{{\underline {\overline {\bf{A}} } }^T}\underline {\overline {\bf{A}} } } \right)} \right|_{\underline {\overline {\bf{A}} } {\rm{ constant}}}} = \left( {{{\underline {\overline {\bf{A}} } }^T} \otimes {{\underline {\overline {\bf{I}} } }_{\left[ n \right]}}} \right){\underline {\overline {\bf{K}} } _{\left[ {m,n} \right]}}$$
I found it a challenge to stitch together all the different results required to do this type of calculation proficiently (which I needed to compute the Jacobian determinant of SVD transformations).  One very useful reference that dealt with elimination and commutation matrices is:
Magnus, J., and Neudecker, H., “The Elimination Matrix:  Some Lemmas and Applications,” SIAM J. on Algebraic. and Discrete Meth., V. 1, Issue 4, pp 422-449, Dec. 1980.
However, this doesn’t cover anything to do with the calculus side of things.  I ended up compiling my own list of useful results, which (for the real case) can be found here in Section 3.  The fact that it is Rev 8 gives you a sense of how easy it is to mess things up.
