ass1: Fix elemental sc plot and add caption

superconductivity_assignment1_kvkempen.tex

@@ -59,8 +59,12 @@ The data on critical temperatures $T_c$ and (approximately) room temperature res
 
 \begin{figure}[H]
 	\includegraphics[width=\textwidth]{sc_elements.pdf}
+	\caption{In this plot of the critical temperature $T_c$ versus the room temperature resistivity $\rho_{300K}$ for elemental superconductors, not one clear relation can be distinguished. For most elements, resistivity is taken at room temperature $T = \SI{300}{\kelvin}$. If it was unavailable in consulted references, the value at the temperature closest to \SI{300}{\kelvin} was chosen. See the table in appendix \ref{appendix:scelements} for the raw data including their source. The mess in the left bottom corner was hard to filter out. A log-log plot was attempted and improved separation, but obscured the observed form.}
 \end{figure}
 
+As a way to quantize the (lack of) linear correlation, the calculated Pearson correlation coefficient $r = 0.165415$, suggesting a slightly positive but uncertain correlation.
+% I used df.corr() to calculate $r$.
+
 \section{Exam question electrodynamics in superconductors}
 No idea yet.