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\subsection{Introduction of numerical analysis}  Students are expected to do their lab work using \ipython\ notebooks. There are several reasons for adopting \texttt{Python}: it is widely used in astronomy; it is easy to learn but supports complex programming; it has powerful libraries---\np, \sp, and \plt---for numerical analysis and plotting; and the \ipython\ notebooks are relatively platform-independent.  Figure~\ref{f.sample-datasets} illustrates an in-class \ipython\ exercise that was used to illustrate the $\chi^2$-test. The students use the notebook to generate fake datsets, compute $\chi^2$ for those datasets, and then answer questions about their findings. The \ipython\ notebooks are uploaded to a course dropbox for grading.