This commit is contained in:
Morten Hjorth-Jensen
2023-08-27 21:47:32 +02:00
parent 782156697d
commit c23ad32c2c
10 changed files with 516 additions and 512 deletions
+8 -8
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@@ -551,11 +551,11 @@ Let now $\bm{y}=\bm{A}\bm{x}$, where $\bm{A}$ is an $m\times n$ matrix and the m
y_i = \sum_{j=0}^{n-1}a_{ij}x_j,
\]
!et
with $\all i=0,1,2,\dots,m-1$. The individual matrix elements of $\bm{A}$ are given by the symbol $a_{ij}$.
with $\forall i=0,1,2,\dots,m-1$. The individual matrix elements of $\bm{A}$ are given by the symbol $a_{ij}$.
It follows that the partial derivatives of $y_i$ with respect to $x_k$
!bt
\[
\frac{\partial y_i }{\partial x_k}= a_{ik} \all i=0,1,2,\dots,m-1.
\frac{\partial y_i }{\partial x_k}= a_{ik} \forall i=0,1,2,\dots,m-1.
\]
!et
@@ -576,7 +576,7 @@ multiplications
!bt
\[
\alpha = \bm{y}^T\bm{A}\bm{x}$,
\alpha = \bm{y}^T\bm{A}\bm{x},
\]
!et
with $\bm{y}$ a vector of length $m$, $\bm{A}$ an $m\times n$ matrix and $\bm{x}$ a vector of length $n$. We assume also that $\bm{A}$ does not depend on any of the two vectors.
@@ -584,7 +584,7 @@ In order to find the derivative of $\alpha$ with respect to the two vectors, we
$\bm{z}^T=\bm{y}^T\bm{A}$, a vector of length $n$. We have then
!bt
\[
\alpha = \bm{z}^T\bm{x}$,
\alpha = \bm{z}^T\bm{x},
\]
!et
which means that (using our previous example) we have
@@ -612,7 +612,7 @@ matrix with dimension $n\times n$.
!bt
\[
\alpha = \bm{x}^T\bm{A}\bm{x}$,
\alpha = \bm{x}^T\bm{A}\bm{x},
\]
!et
with $\bm{x}$ a vector of length $n$.
@@ -620,7 +620,7 @@ with $\bm{x}$ a vector of length $n$.
We write out the specific sums involved in the calculation of $\alpha$
!bt
\[
\alpha = \sum_{i=0}^{n-1}\sum_{j=0}^({n-1}x_i a_{ij}x_j,
\alpha = \sum_{i=0}^{n-1}\sum_{j=0}^{n-1}x_i a_{ij}x_j,
\]
!et
taking the derivative of $\alpha$ with respect to a given component $x_k$ we get the two sums
@@ -629,7 +629,7 @@ taking the derivative of $\alpha$ with respect to a given component $x_k$ we get
\frac{\partial \alpha}{\partial x_k} = \sum_{i=0}^{n-1}a_{ik}x_i+\sum_{j=0}^{n-1}a_{kj}x_j,
\]
!et
for $\all k =0,1,2,\dots,n-1$. We identify these sums as
for $\forall k =0,1,2,\dots,n-1$. We identify these sums as
!bt
\[
\frac{\partial \alpha}{\partial \bm{x}} = \bm{x}^T\left(\bm{A}^T+\bm{A}\right).
@@ -670,7 +670,7 @@ and the partial derivative
\frac{\partial \alpha}{\partial z_k} = \sum_{i=0}^{n-1}\left(x_i\frac{\partial y_i}{\partial z_k}+y_i\frac{\partial x_i}{\partial z_k}\right),
\]
!et
for $\all k =0,1,2,\dots,n-1$. We can rewrite the partial derivative in a more compact form as
for $\forall k =0,1,2,\dots,n-1$. We can rewrite the partial derivative in a more compact form as
!bt
\[
\frac{\partial \alpha}{\partial \bm{z}} = \bm{x}^T\frac{\partial \bm{y}}{\partial \bm{z}}+\bm{y}^T\frac{\partial \bm{x}}{\partial \bm{z}},