pep-material: comparison cws/cw01.tex

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-:59779ce322a6
+:ca48ac1d3c3e
 \mbox{}\hfill\textit{coupled with judiciously placed print statements.''}\smallskip\\
 \mbox{}\hfill\textit{ --- Brian W. Kernighan, in Unix for Beginners (1979)}\bigskip
 \noindent
-This assignment is about Scala and worth 10\%. The first and second
+This assignment is about Scala and worth 10\%. The basic
-part are due on \cwSIX{} at 11pm, and the third part on \cwSIXa{}
+part is due on \cwSIX{} at 11pm, and the main part on \cwSIXa{}
 at 11pm. You are asked to implement two programs about list
-processing and recursion. The third part is more advanced and might
+processing and recursion. The main part is more advanced and might
 include material you have not yet seen in the first lecture.
 \bigskip
 \IMPORTANT{}
 \subsection*{Reference Implementation}
 Like the C++ assignments, the Scala assignments will work like this: you
 push your files to GitHub and receive (after sometimes a long delay) some
 automated feedback. In the end we take a snapshot of the submitted files and
-apply an automated marking script to them.
+apply an automated marking script to them.\medskip
+\noindent
 In addition, the Scala assignments come with a reference implementation
 in form of a \texttt{jar}-file. This allows you to run any test cases
 on your own computer. For example you can call Scala on the command
 line with the option \texttt{-cp collatz.jar} and then query any
 function from the template file. Say you want to find out what
 \texttt{.toList} for conversions, \texttt{List(...).max} for the
 maximum of a list, \texttt{List(...).indexOf(...)} for the first index of
 a value in a list.\bigskip
 \noindent
-\textbf{For Part 2 + 3:} useful string functions: \texttt{.startsWith(...)} for
+\textbf{For Part 2:} useful string functions:
-checking whether a string has a given prefix, \texttt{\_ ++ \_} for
+\texttt{.startsWith(...)} for checking whether a string has a given
-concatenating two strings; useful option functions: \texttt{.flatten}
+prefix, \texttt{\_ ++ \_} for concatenating two strings; useful option
-flattens a list of options such that it filters way all
+functions: \texttt{.flatten} flattens a list of options such that it
-\texttt{None}'s, \texttt{Try(...).getOrElse ...} runs some code that
+filters way all \texttt{None}'s, \texttt{Try(...).getOrElse ...} runs
-might raise an exception---if yes, then a default value can be given;
+some code that might raise an exception---if yes, then a default value
-useful list functions: \texttt{.head} for obtaining the first element
+can be given; useful list functions: \texttt{.head} for obtaining the
-in a non-empty list, \texttt{.length} for the length of a
+first element in a non-empty list, \texttt{.length} for the length of
-list; \texttt{.filter(...)} for filtering out elements in a list; \texttt{.getLines.toList} for obtaining a list of lines from
+a list; \texttt{.filter(...)} for filtering out elements in a list;
-a file; \texttt{.split(",").toList} for splitting strings according to
+\texttt{.getLines.toList} for obtaining a list of lines from a file;
-a comma.\bigskip
+\texttt{.split(",").toList} for splitting strings according to a
+comma.\bigskip
-\noindent
-Fortunately Scala supports operator overloading. But make sure you understand the difference between \texttt{100 / 3} and
+\noindent
+\textbf{Note!} Fortunately Scala supports operator overloading. But
+make sure you understand the difference between \texttt{100 / 3} and
 \texttt{100.0 / 3}!
 \newpage
-\subsection*{Part 1 (3 Marks, file collatz.scala)}
+\subsection*{Basic Part (3 Marks, file collatz.scala)}
 This part is about recursion. You are asked to implement a Scala
 program that tests examples of the \emph{$3n + 1$-conjecture}, also
 called \emph{Collatz conjecture}. This conjecture can be described as
 follows: Start with any positive number $n$ greater than $0$:
 1$.
 \item Repeat this process and you will always end up with $1$.
 \end{itemize}
 \noindent
-For example if you start with $6$, or $9$, you obtain the
+For example if you start with, say, $6$ and $9$, you obtain the
-series
+two series
 \[
 \begin{array}{@{}l@{\hspace{5mm}}l@{}}
 6, 3, 10, 5, 16, 8, 4, 2, 1 & \text{(= 8 steps)}\\
 9, 28, 14, 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1  & \text{(= 19 steps)}\\
 this will \emph{always} happen for every number greater than
 0.\footnote{While it is relatively easy to test this conjecture with
 particular numbers, it is an interesting open problem to
 \emph{prove} that the conjecture is true for \emph{all} numbers ($>
 0$). Paul Erd\"o{}s, a famous mathematician you might have hard
-about, said about this conjecture: ``Mathematics may not be ready
+about, said about this conjecture: ``Mathematics may not [yet] be ready
 for such problems.'' and also offered a \$500 cash prize for its
 solution. Jeffrey Lagarias, another mathematician, claimed that
 based only on known information about this problem, ``this is an
 extraordinarily difficult problem, completely out of reach of
 present day mathematics.'' There is also a
-\subsection*{Part 2 (3 Marks, file drumb.scala)}
+\subsection*{Main Part (7 Marks, file drumb.scala)}
 A purely fictional character named Mr T.~Drumb inherited in 1978
 approximately 200 Million Dollar from his father. Mr Drumb prides
 himself to be a brilliant business man because nowadays it is
 estimated he is 3 Billion Dollar worth (one is not sure, of course,
 \item Next year in January, we look at how our stocks did, liquidate
 everything, and re-invest our (hopefully) increased money in again
 the stocks from our portfolio (there might be more stocks available,
 if companies from our portfolio got listed in that year, or less if
 some companies went bust or were de-listed).
-\item We do this for 40 years until January 2018 and check what would
+\item We do this for 40 years until January 2019 and check what would
 have become out of our \$100.
 \end{itemize}
 \noindent
-Until Yahoo was bought by Altaba last year, historical stock market
+Until Yahoo was bought by Altaba a few years ago, historical stock market
 data for such back-of-the-envelope calculations was freely available
 online. Unfortunately nowadays this kind of data is more difficult to
 obtain, unless you are prepared to pay extortionate prices or be
 severely rate-limited.  Therefore this assignment comes with a number
 of files containing CSV-lists with the historical stock prices for the
 lists are for all stock symbols from the portfolio and the outer
 list for the years.  For example for Google and Apple in years 2010
 (first line), 2011 (second line) and 2012 (third line) you obtain:
 \begin{verbatim}
-List(List(Some(311.349976), Some(20.544939)),
+List(List(Some(312.204773), Some(26.782711)),
-List(Some(300.222351), Some(31.638695)),
+List(Some(301.0466),   Some(41.244694)),
-List(Some(330.555054), Some(39.478039)))
+List(Some(331.462585), Some(51.464207)))
 \end{verbatim}\hfill[1 Mark]
-\end{itemize}
-\subsection*{Advanced Part 3 (4 Marks, continue in file drumb.scala)}
+%\end{itemize}
-\noindent
+%\subsection*{Advanced Part 3 (4 Marks, continue in file drumb.scala)}
-\textbf{Tasks}
+%
+%\noindent
-\begin{itemize}
+%\textbf{Tasks}
+%\begin{itemize}
 \item[(4)] Write a function that calculates the \emph{change factor} (delta)
 for how a stock price has changed from one year to the next. This is
 only well-defined, if the corresponding company has been traded in both
 years. In this case you can calculate
 If the change factor is defined, you should return it
 as \texttt{Some(change\_factor)}; if not, you should return
 \texttt{None}.\mbox{}\hfill\mbox{[1 Mark]}
 \item[(5)] Write a function that calculates all change factors
-(deltas) for the prices we obtained under Part 2. For the running
+(deltas) for the prices we obtained in Task (2). For the running
 example of Google and Apple for the years 2010 to 2012 you should
 obtain 4 change factors:
 \begin{verbatim}
-List(List(Some(-0.03573992567129673), Some(0.539975124774038))
+List(List(Some(-0.03573991804411003), Some(0.539974575389325)),
-List(Some(0.10103412653643493), Some(0.24777709700099845)))
+List(Some(0.10103414222249969), Some(0.24777764141006836)))
 \end{verbatim}
 That means Google did a bit badly in 2010, while Apple did very well.
 Both did OK in 2011. Make sure you handle the cases where a company is
 not listed in a year. In such cases the change factor should be \texttt{None}
-(see~(4)).
+(recall Task~(4)).
 \mbox{}\hfill\mbox{[1 Mark]}
 \item[(6)] Write a function that calculates the ``yield'', or
 balance, for one year for our portfolio.  This function takes the
 change factors, the starting balance and the year as arguments. If
 no company from our portfolio existed in that year, the balance is
 unchanged. Otherwise we invest in each existing company an equal
 amount of our balance. Using the change factors computed under Task
-2, calculate the new balance. Say we had \$100 in 2010, we would have
+(2), calculate the new balance. Say we had \$100 in 2010, we would have
 received in our running example involving Google and Apple:
 \begin{verbatim}
-$50 * -0.03573992567129673 + $50 * 0.539975124774038
+$50 * -0.03573991804411003 + $50 * 0.539974575389325
-= $25.21175995513706
+= $25.21173286726075
 \end{verbatim}
 as profit for that year, and our new balance for 2011 is \$125 when
 converted to a \texttt{Long}.\mbox{}\hfill\mbox{[1 Mark]}
 \noindent
 \textbf{Test Data:} File \texttt{drumb.scala} contains two portfolios
 collected from the S\&P 500, one for blue-chip companies, including
 Facebook, Amazon and Baidu; and another for listed real-estate
 companies, whose names I have never heard of. Following the dumb
-investment strategy from 1978 until 2018 would have turned a starting
+investment strategy from 1978 until 2019 would have turned a starting
-balance of \$100 into roughly \$101,589 for real estate and a whopping
+balance of \$100 into roughly \$39,162 for real estate and a whopping
-\$1,587,528 for blue chips.  Note when comparing these results with your
+\$462,199 for blue chips.  Note when comparing these results with your
 own calculations: there might be some small rounding errors, which
 when compounded lead to moderately different values.\bigskip
 \noindent

changeset 266	ca48ac1d3c3e
parent 252	a9d84442fb65
child 276	52faee6d0be2