kugel: Re-add usecase reference, minor corrections

2 files changed, 31 insertions, 6 deletions

diff --git a/buch/papers/kugel/references.bib b/buch/papers/kugel/references.bib
index e13b67c..7603f2f 100644
--- a/buch/papers/kugel/references.bib
+++ b/buch/papers/kugel/references.bib
@@ -275,4 +275,20 @@ This photo was taken during studies that resulted in the publication: Hope, C, S
 	urldate = {2022-08-27},
 	date = {2022-04-27},
 	doi = {10.5281/ZENODO.6497293},
+}
+
+@article{davari_new_2013,
+	title = {New Implementation of Legendre Polynomials for Solving Partial Differential Equations},
+	volume = {04},
+	issn = {2152-7385, 2152-7393},
+	url = {http://www.scirp.org/journal/doi.aspx?DOI=10.4236/am.2013.412224},
+	doi = {10.4236/am.2013.412224},
+	pages = {1647--1650},
+	number = {12},
+	journaltitle = {Applied Mathematics},
+	shortjournal = {{AM}},
+	author = {Davari, Ali and Ahmadi, Abozar},
+	urldate = {2022-08-28},
+	date = {2013},
+	file = {Full Text:/Users/npross/Zotero/storage/A8XM56WK/Davari and Ahmadi - 2013 - New Implementation of Legendre Polynomials for Sol.pdf:application/pdf},
 }
\ No newline at end of file
diff --git a/buch/papers/kugel/spherical-harmonics.tex b/buch/papers/kugel/spherical-harmonics.tex
index 02d93e9..0fb6557 100644
--- a/buch/papers/kugel/spherical-harmonics.tex
+++ b/buch/papers/kugel/spherical-harmonics.tex
@@ -190,7 +190,6 @@ require a dedicated section of its own.
 
 \begin{figure}
   \centering
-  % \kugelplaceholderfig{.8\textwidth}{5cm}
   \includegraphics[
     scale = 1.2,
     trim = 0 40 0 0, clip,
@@ -327,7 +326,14 @@ obtain the \emph{associated Legendre functions}.
   \end{equation}
   are known as Ferrers or associated Legendre functions.
 \end{definition}
-The constraint $|m|<n$, can be justified by considering eq.\eqref{kugel:eq:associated_leg_func}, where we differentiate $m+n$ times. We all know that a differentiation, to be well defined, must have an order that is greater than zero \kugeltodo{is that always true?}. Furthermore, it can be seen that this derivative is applied on a polynomial of degree $2n$. As is known from Calculus 1, if you derive a polynomial of degree $2n$ more than $2n$ times, you get zero, that would be a trivial solution. This is the power of zero: It is almost always a (boring) solution.
+The constraint $|m|<n$, can be justified by considering equation
+\eqref{kugel:eq:associated_leg_func}, where we differentiate $m+n$ times. We all
+know that a differentiation, to be well defined, must have an order that is
+greater than zero. Furthermore, it can be seen that this derivative is applied
+on a polynomial of degree $2n$. As is known from Calculus 1, if you derive a
+polynomial of degree $2n$ more than $2n$ times, you get zero, that would be a
+trivial solution. This is the power of zero: It is almost always a (boring)
+solution.
 
 We can thus summarize these two conditions by writing:
 \begin{equation*}
@@ -344,8 +350,8 @@ section \ref{kugel:sec:construction:eigenvalue}. We had left off in the middle
 of the separation, were we had used the Ansatz $f(\vartheta, \varphi) =
 \Theta(\vartheta) \Phi(\varphi)$ to find that $\Phi(\varphi) = e^{im\varphi}$,
 and we were solving for $\Theta(\vartheta)$.  As you may recall, previously we
-performed the substitution $z = \cos \vartheta$. Now we can finally bring back the
-solution to the associated Legendre equation $P^m_n(z)$ into the $\vartheta$
+performed the substitution $z = \cos \vartheta$. Now we can finally bring back
+the solution to the associated Legendre equation $P^m_n(z)$ into the $\vartheta$
 domain and combine it with $\Phi(\varphi)$ to get the full result:
 \begin{equation*}
     f(\vartheta, \varphi)
@@ -709,8 +715,11 @@ To start this journey, we can first write the following equations, which relate
 \end{subequations}
 Much of the effort will be proving this bunch of equalities. Then, in the second part, where we will derive the recursion equations for $Y^m_n(\vartheta,\varphi)$, we will basically reuse the ones presented above.
 
-Maybe it is worth mentioning at least one use case for these relations: In some software implementations (that include lighting computations in computer graphics, antenna modelling softwares, 3-D modelling in medical applications, etc.) 
-they are widely used, as they lead to better numerical accuracy and computational cost lower by a factor of six\cite{usecase_recursion_paper}. 
+Maybe it is worth mentioning at least one use case for these relations: In some
+software implementations (that include lighting computations in computer
+graphics, antenna modelling software, 3-D modelling in medical applications,
+etc.) they are widely used, as they lead to better numerical accuracy and
+computational cost lower by a factor of six \cite{davari_new_2013}.
 \begin{enumerate}[(i)]
   \item 
   \begin{proof}