It's me again, guy aged 45 thinking about doing graduate work in CS. I read this ebook about a guy's CS PhD, "The PhD Grind":It was enlightening. I used to think that software in the C.S. academic world must be wellwritten, seeing as it was written by computer scientists. (I didn't like the poorly organized and simpleminded code involved in my last job at NASA.) Turns out that academic code can be very poor indeed, sometimes just a hacked prototype meant to demonstrate an idea to get it published. It may be the youngest PhD students who are assigned the job of cranking out such prototypes. So what do I want to do for my life's work, once I can overcome this illness and get back to work fulltime? I hope I can work with beauty in some form. I find Haskell to be beautiful, for instance. I like ideas, but I also like the process of implementing ideas in a quality way. I may not be suited to the academic world because I need to spend at least some of my time as a craftsman of code, doing something well. Is there an area with CS academia that is more about elegance, less about hacking up prototypes? The study of languages? Second, what if I thought of PhD not as a way to enter academia, but as a way to qualify me for the more interesting and creative C.S. jobs out there? What kinds of C.S. jobs involve real creative control, an opportunity to do things in an elegant way? I know that's a very broad question, so maybe those reading could mention single examples or things they've run into. No need to cover everything. Thanks, Dennis _______________________________________________ HaskellCafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskellcafe 
the best way to get cool work is to create opportunities! Do great work and make it visible, reach out to businesses. etc while theres many people on haskell cafe who are happy to try to give advice, i think we're the wrong group to give advice.
1) reach out to your universities alumni network, there'll be many folks in many organizations who may be willing to help / give you advice 2) email organizations that are hiring that you're excited by and where you have some basic fluency in the the skills they need. The fact of the matter is that for jumpstarting/resuming a career thats been on hiatus, taking a junior role is the best way to get it started. One good listing that happens every month is the hacker news who's hiring thread, and they list many remote ok jobs too!
best of luck _Carter On Sat, Dec 7, 2013 at 6:54 PM, Dennis Raddle <[hidden email]> wrote:
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In reply to this post by Dennis Raddle
On 8/12/2013, at 12:54 PM, Dennis Raddle wrote: > It's me again, guy aged 45 thinking about doing graduate work in CS. > > I read this ebook about a guy's CS PhD, "The PhD Grind": > > <http://www.pgbovine.net/PhDmemoir.htm> > > It was enlightening. I used to think that software in the C.S. academic world must be wellwritten, seeing as it was written by computer scientists. There is a huge difference between *computer science* and *programming*. I remember two excellent computer scientists I used to know, neither of whom had any idea of indentation. (Seriously, one of them began each function on a new line, and pressed the RETURN key only at the very end of it.) Come to think of it, I met another computer scientist who was writing a library for an exotic flavour of priority queue  which he understood to a depth I shall never reach  and was interested in comparing it against some other priority queue implementations, and asked me for some advice about the coding. I suggested including the classic binaryheapinan array as a baseline. It beat the pants off _all_ the other priority queue implementations. Here's a piece of computer science that I would like some help with. I call it the Indirect Cycle Detection problem. Given: Domains P and E, functions f : P > Maybe P g : P > E Define to_list :: Maybe P > [E] to_list Nothing = [] to_list (Just p) = g p : to_list (f p) Given: That f is cyclic starting at p0. Find: The shortest alpha, beta such that to_list p0 is alpha ++ cycle beta and do so *efficiently*. Now, I can use tortoiseandhare to find a cycle in f and then use brute force to find a shortest prefix and cycle of to_list ... The stuff I've checked so far about periods in strings has nothing to say about periods that begin _after_ a nonempty prefix. The point here is that this is a computer science question which can be answered by someone who has no knowledge of any programming language. Indeed, I don't see any reason to expect that programming skill would help. > (I didn't like the poorly organized and simpleminded code involved in my last job at NASA.) And yet we hear amazing things about NASA code quality. > Turns out that academic code can be very poor indeed, sometimes just a hacked prototype meant to demonstrate an idea to get it published. Since the declared *aim* of Universities is *published* research, it is *rational* for code quality to be no higher than is required to get that job done. Basically, Sturgeon's Revelation  see http://http://en.wikipedia.org/wiki/Sturgeon's_Law  is a universal truth. I remember a certain company whose compilers and operating system were gems of care and readability, yet provided a statistics package whose code was _nightmarish_, pointlessly bulky, and would happily invert a singular matrix and keep running. Had you considered building software checking tools as a topic? _______________________________________________ HaskellCafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskellcafe 
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On Sun, Dec 8, 2013 at 5:24 AM, Dennis Raddle <[hidden email]> wrote:
about beauty in mathematical proofs [And in case you wonder what that has to do with CS  the guide was E W Dijkstra] _______________________________________________ HaskellCafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskellcafe 
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On Sat, Dec 7, 2013 at 5:54 PM, Dennis Raddle <[hidden email]> wrote:
In that case, it can be helpful to use the right license: http://matt.might.net/articles/crapl/CRAPLLICENSE.txt
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On Sun, Dec 8, 2013 at 6:54 AM, Dennis Raddle <[hidden email]> wrote:
Beauty is very much in the eye of the beholder. Have you looked at "Land the Tech Job You Love" by the Pragmatic label? Chapter 1 might be free and well worth the read, approx 10 pages. Something that strikes me about your emails is that you're focused on your wants and needs. Which is important. But a job is ultimately a trade: you give up X in return for Y. Grad school these days is no different; admissions DO actively look for that X, even if that X is different from that of a commercial setting. Think about what those X's might be  as in, what does the other party want. Feel free to continue the convo on this list!  KimEe _______________________________________________ HaskellCafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskellcafe 
In reply to this post by Richard A. O'Keefe
Hi Richard,
Am 09.12.2013 04:00, schrieb Richard A. O'Keefe: > > [...] > Here's a piece of computer science that I would like some help > with. I call it the Indirect Cycle Detection problem. > > Given: Domains P and E, > functions f : P > Maybe P > g : P > E > > Define to_list :: Maybe P > [E] > to_list Nothing = [] > to_list (Just p) = g p : to_list (f p) > > Given: That f is cyclic starting at p0. > > Find: The shortest alpha, beta such that > to_list p0 is alpha ++ cycle beta > and do so *efficiently*. > > Now, I can use tortoiseandhare to find a cycle in f > and then use brute force to find a shortest prefix and > cycle of to_list ... The stuff I've checked so far > about periods in strings has nothing to say about > periods that begin _after_ a nonempty prefix. > I am not sure if you're really looking for help here or just wanted to present an example. I assume the former. Also, I can not see where this "nonempty prefix" notion comes from. Perhaps you have a different definition for cyclic? For me: "f is cyclic starting at p0" means there exist an N>0 such that f^N p0 == p0. Let's assume n to be the smallest number that fulfills this condition and call it the period length of f_p0. f_p0 defines a periodic list ps with the same period length n. ps = map fromJust $ iterate (>>= f) (Just p0) Your (to_list p0), which I'd like to call es could now be written as: es = map g ps We know that es has a period of length n, but if g is not injective, its smallest period of length k may be smaller than n. period_n = take n es To find k, we search for the second occurrence of period_n in (period_n ++ period_n), knowing that it will be at position n, if it is not found at positions [1..n1]. We might use the fact that it can only be in positions that divide n. On the other hand, we could just use any of the well known stringsearchmethods. Efficiency:  If computation of f is done in constant time, finding n takes Theta(n) time. Just apply f until you reach p0 again.  Searching a pattern of size n in a text of size 2n can be done in O(n) using the KnuthMorrisPrattalgorithm. In total you have a linear algorithm for finding your result: alpha = [] beta = take k es = take k period_n ***** Of course, I guess now you're going to tell me that your "nonempty prefix" means that the period of f is not starting at p0 but at some pi that is reached by applying f i times to p0. You can adapt to that, but you have to pay for it ;) In this case, ps has the form (prefix ++ (cycle p_period_n)) and to find this structure, you need to find the first element of ps that occurs twice. (Before, you knew this would be p0.) For that, you need a set implementation for elements of P that gives you efficient adding of one element and lookup. Since we know nothing about P's elements, we use the list itself and get a runtime of Theta((i+n)^2). Finding the (smallest) period k in es is exactly the same as before, i.e. we look for the second occurrence of period_n in (period_n ++ period_n) with period_n = map g p_period_n The prefix does not bother us here, because we know that we are looking at the periodic part. Now that we know the period length k, we still have to find where it starts. For that we start at position i and go backwards until we find a difference to the found out period. That is, we find the position of the first mismatch between (reverse $ take i es) and (cycle (reverse $ take k period_n)). The index tells us the length of alpha and the rotation needed to get beta from (take k period_n). The cost for that is O(i). So, the total cost in this case would be O((i+n)^2 + n + i). I could have implemented this in Haskell, but since the point in the original discussion was about not needing programmer skills, but CS skills, I refrained from it. Haskell is only used to clarify points, in a language which both he recipient and the recipient know. :) Thomas _______________________________________________ HaskellCafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskellcafe 
Hi Thomas and Richard,
> > [...] > >Here's a piece of computer science that I would like some help > >with. I call it the Indirect Cycle Detection problem. > > > >Given: Domains P and E, > > functions f : P > Maybe P > > g : P > E > > > >Define to_list :: Maybe P > [E] > > to_list Nothing = [] > > to_list (Just p) = g p : to_list (f p) > > > >Given: That f is cyclic starting at p0. > > > >Find: The shortest alpha, beta such that > > to_list p0 is alpha ++ cycle beta > > and do so *efficiently*. > > > >Now, I can use tortoiseandhare to find a cycle in f > >and then use brute force to find a shortest prefix and > >cycle of to_list ... The stuff I've checked so far > >about periods in strings has nothing to say about > >periods that begin _after_ a nonempty prefix. will identify a tail of the sequence that is known to be periodic, and then we can find the smallest period using an algorithm that operates on a finite string. Once the actual cycle length is known, identifying the prefix is easy. > Also, I can not see where this "nonempty prefix" notion comes from. > Perhaps you have a different definition for cyclic? See http://en.wikipedia.org/wiki/Cycle_detection . > In this case, ps has the form (prefix ++ (cycle p_period_n)) and to > find this structure, you need to find the first element of ps that > occurs twice. (Before, you knew this would be p0.) For that, you > need a set implementation for elements of P that gives you efficient > adding of one element and lookup. Since we know nothing about P's > elements, we use the list itself and get a runtime of > Theta((i+n)^2). The tortoiseandhare algorithm does this in O(i+n) time. I'm attaching some code. For simplicity, it works with functions @f :: a > a@, @g :: a > b@, which define the sequence @xs = map g (iterate f x)@. I'm using Brent's algorithm [1] for cycle detection, which finds the period and a periodic suffix of @iterate f x@, followed by Duval's algorithm [2] to identify the actual cycle length of @xs@. (The main advantage of Duval's algorithm over KnuthMorrisPratt is that less space is required. One disadvantage is that we need a total order on @b@.) The total running time is linear in the cycle length and initial prefix length of @iterate f x@, i.e. O(i+n). There are two entry points of interest in the code.  factor f g x Find prefix and repeated segment of @map g (iterate f x)@.  factor' f g x Find prefix and repeated segment of @to_list x@. The repeated segment will be empty if @to_list x@ is a finite list. Cheers, Bertram [1] http://en.wikipedia.org/wiki/Cycle_detection [2] http://stackoverflow.com/questions/3459509/minimalcyclicshiftalgorithmexplanation _______________________________________________ HaskellCafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskellcafe duval.hs (1K) Download Attachment 
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