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• SQLAlchemy custom sorting algorithms when using SQL indexes

  - by David M

  Is it possible to write custom collation functions with indexes in SQLAlchemy? SQLite for example allows specifying the sorting function at a C level as sqlite3_create_collation(). An implementation of some of the Unicode collation algorithm has been provided by James Tauber here, which for example sorts all the "a"'s close together whether they have accents on them or not. Other examples of why this might be useful is for different alphabet orders (languages other than English) and sorting numeric values (sorting 10 after 9 rather than codepoint order.) Is this possible in SQLAlchemy? If not, is it supported by the pysqlite3 or MySQLdb modules, or for any other SQL database modules supported by python for that matter? Any information would be greatly appreciated.

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• Why is win32com so much slower than xlrd?

  - by Josh

  I have the same code, written using win32com and xlrd. xlrd preforms the algorithm in less than a second, while win32com takes minutes. Here is the win32com: def makeDict(ws): """makes dict with key as header name, value as tuple of column begin and column end (inclusive)""" wsHeaders = {} # key is header name, value is column begin and end inclusive for cnum in xrange(9, find_last_col(ws)): if ws.Cells(7, cnum).Value: wsHeaders[str(ws.Cells(7, cnum).Value)] = (cnum, find_last_col(ws)) for cend in xrange(cnum + 1, find_last_col(ws)): #finds end column if ws.Cells(7, cend).Value: wsHeaders[str(ws.Cells(7, cnum).Value)] = (cnum, cend - 1) break return wsHeaders And the xlrd def makeDict(ws): """makes dict with key as header name, value as tuple of column begin and column end (inclusive)""" wsHeaders = {} # key is header name, value is column begin and end inclusive for cnum in xrange(8, ws.ncols): if ws.cell_value(6, cnum): wsHeaders[str(ws.cell_value(6, cnum))] = (cnum, ws.ncols) for cend in xrange(cnum + 1, ws.ncols):#finds end column if ws.cell_value(6, cend): wsHeaders[str(ws.cell_value(6, cnum))] = (cnum, cend - 1) break return wsHeaders

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• Performance optimization strategies of last resort?

  - by jerryjvl

  There are plenty of performance questions on this site already, but it occurs to me that almost all are very problem-specific and fairly narrow. And almost all repeat the advice to avoid premature optimization. Let's assume: the code already is working correctly the algorithms chosen are already optimal for the circumstances of the problem the code has been measured, and the offending routines have been isolated all attempts to optimize will also be measured to ensure they do not make matters worse What I am looking for here is strategies and tricks to squeeze out up to the last few percent in a critical algorithm when there is nothing else left to do but whatever it takes. Ideally, try to make answers language agnostic, and indicate any down-sides to the suggested strategies where applicable. I'll add a reply with my own initial suggestions, and look forward to whatever else the SO community can think of.

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• Pure Java open-source libraries for portfolio selection (= constrained, non-linear optimization)?

  - by __roland__

  Does anyone know or has experience with a pure Java library to select portfolios or do some similar kinds of quadratic programming with constraints? There seems to be a lot of tools, as already discussed elsewhere - but what I would like to use is a pure Java implementation. Since I want to call the library from within another open-source software with a BSD-ish license I would prefer LGPL over GPL. Any help is appreciated. If you don't know such libraries, which is the most simple algorithm you would suggest to implement? It has to cope with an inequality constraint (all x_i = 0) and an equality constraint (sum of all x_i = 1).

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• Candidate Elimination Question---Please help!

  - by leon

  Hi , I am doing a question on Candidate Elimination Algorithm. I am a little confused with the general boundary G. Here is an example, I got G and S to the fourth case, but I am not sure with the last case. Sunny,Warm,Normal,Strong,Warm,Same,EnjoySport=yes Sunny,Warm,High,Strong,Warm,Same,EnjoySport=yes Rainy,Cold,High,Strong,Warm,Change,EnjoySport=no Sunny,Warm,High,Strong,Cool,Change,EnjoySport=yes Sunny,Warm,Normal,Weak,Warm,Same,EnjoySport=no What I have here is : S 0 :{0,0,0,0,0,0} S 1 :{Sunny,Warm,Normal,Strong,Warm,Same} S 2 , S 3 : {Sunny,Warm,?,Strong,Warm,Same} S 4 :{Sunny,Warm,?,Strong,?,?} G 4 :{Sunny,?,?,?,?,?,?,Warm,?,?,?,?} G 3 :{Sunny,?,?,?,?,?,?,Warm,?,?,?,?,?,?,?,?,?,Same} G 0 , G 1 , G 2 : {?,?,?,?,?,?} What would be the result of G5? Is it G5 empty? {}? or {???Strong??) ? Thanks

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• Encode/compress sequence of repeating integers

  - by Alex

  Hey there! I have very long integer sequences that look like this (arbitrary length!): 0000000001110002220033333 Now I need some algorithm to convert this string into something compressed like a9b3a3c3a2d5 Which means "a 9 times, then b 3 times, then a 3 times" and so on, where "a" stands for 0, "b" for 1, "c" for 2 and "d" for 3. How would you do that? So far nothing suitable came to my mind, and I had no luck with google because I didn't really know what to search for. What is this kind of encoding / compression called? PS: I am going to do the encoding with PHP, and the decoding in JavaScript.

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• Memcache failover and consistent hashing

  - by Industrial

  Hi everyone, I am trying to work out a good way to handle offline/down memcached servers in my current web application that are built with PHP. I just found this link that shows an approach on how to do what I want, I think: http://cmunezero.com/2008/08/11/consistent-memcache-hashing-and-failover-with-php/ Anyhow, it gets me confused when I start working with it and reading the PHP documention about failover with memcache. Why is offline memcache servers added to the $realInstance server pool together with the online servers? Reading the memcache documentation confuses me even more: http://www.php.net/manual/en/memcache.addserver.php status Controls if the server should be flagged as online. Setting this parameter to FALSE and retry_interval to -1 allows a failed server to be kept in the pool so as not to affect the key distribution algorithm. Requests for this server will then failover or fail immediately depending on the memcache.allow_failover setting. Default to TRUE, meaning the server should be considered online. Thanks,

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• In Haskell, how can you sort a list of infinite lists of strings?

  - by HaskellNoob

  So basically, if I have a (finite or infinite) list of (finite or infinite) lists of strings, is it possible to sort the list by length first and then by lexicographic order, excluding duplicates? A sample input/output would be: Input: [["a", "b",...], ["a", "aa", "aaa"], ["b", "bb", "bbb",...], ...] Output: ["a", "b", "aa", "bb", "aaa", "bbb", ...] I know that the input list is not a valid haskell expression but suppose that there is an input like that. I tried using merge algorithm but it tends to hang on the inputs that I give it. Can somebody explain and show a decent sorting function that can do this? If there isn't any function like that, can you explain why? In case somebody didn't understand what I meant by the sorting order, I meant that shortest length strings are sorted first AND if one or more strings are of same length then they are sorted using < operator. Thanks!

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• PHP Code to Generate Simple Flowchart

  - by revbackup

  I am making a flowchart out the subjects in the curriculum of our school. a flowchart is generated through its preRequisite.... for example FIRST YEAR FIRST SEMESTER SUBJECTS ---- PREREQUISITE MATH 1 ---- NONE MATH 2 ---- NONE ENGL 1 ---- NONE SOCIO 1 ----- NONE POLSCI 1 ----- NONE FIRSTE YEAR SECOND SEMESTER SUBJECTS ---- PREREQUISITE MATH 3 ----- MATH 1 MATH 4 ----- MATH 2, MATH 1 ENGL 2 ----- ENGL 1 POLSCI 2 ----- POLSCI 1 So, I must print it this way, just using simple PHP but difficult Logic.: MATH1 -----> MATH3 -----> MATH4 MATH 2 ----->MATH 4 ENGL1 -----> ENGL 2 SOCIO 1 POLSCI 1 -----> POLSCI 2 Can anyone give me a good algorithm for this, because this is really difficult. I am planning to echo the results in an HTML table, and it makes it more complicated. Do you have suggestions how to solve this problem properly and display the results also properly???? Thank you in advance!

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• Python ValueError: not allowed to raise maximum limit

  - by Ricky Bobby

  I'm using python 2.7.2 on mac os 10.7.3 I'm doing a recursive algorithm in python with more than 50 000 recursion levels. I tried to increase the maximum recursion level to 1 000 000 but my python shell still exit after 18 000 recursion levels. I tried to increase the resources available : import resource resource.setrlimit(resource.RLIMIT_STACK, (2**29,-1)) sys.setrecursionlimit(10**6) and I get this error : Traceback (most recent call last): File "<pyshell#58>", line 1, in <module> resource.setrlimit(resource.RLIMIT_STACK,(2**29,-1)) ValueError: not allowed to raise maximum limit I don't know why I cannot raise the maximum limit ? thanks for your suggestions .

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• Document ranking strategy for P2P file sharing system.

  - by ablmf

  Recently, I got a task of building a P2P file sharing system. There is one requirement : the system should have a document ranking algorithm so that it could be used help users find more valuable files. Several strategy might be useful : force user to give a score to a file before it was downloaded The documents containing certain key words would get higher rank Manager could modify file ranking manually the more a file was downloaded, it would get a higher rank. Do you know any other strategy or methods that also appropriate? Or is there any real world example?

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• Counting viable sublist lengths from an array.

  - by Ben B.

  This is for a genetic algorithm fitness function, so it is important I can do this as efficiently as possible, as it will be repeated over and over. Lets say there is a function foo(int[] array) that returns true if the array is a "good" array and false if the array is a "bad" array. What makes it good or bad does not matter here. Given the full array [1,6,8,9,5,11,45,16,9], lets say that subarray [1,6,8] is a "good" array and [9,5,11,45] is a "good" array. Furthermore [5,11,45,16,9] is a "good" array, and also the longest "good" subarray. Notice that while [9,5,11,45] is a "good" array, and [5,11,45,16,9] is a "good" array, [9,5,11,45,16,9] is a "bad" array. We wants the length counts of all "good" arrays, but not subarrays of "good" arrays. Furthermore, as described above, a "good" array might begin in the middle of another "good" array, but the combination of the two might be a "bad" array.

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• Is there a sample set of web log data available for testing analysis against?

  - by Peter

  Sorry if this isn't strictly speaking a programming question, but I figure my best chance of success would be to ask here. I'm developing some web log file analysis algorithms, but to date I only have access to a fairly small amount of web log data to process. One algorithm I want to use makes some assumptions about 'the shape' of typical web log data, and so I'd like to test it against a larger 'exemplar' - perhaps the logs of a busy site with a good distribution of traffic from different sources etc. Is there a set of such data available somewhere? Thanks for any help.

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• how to pass an arbitrary signature to Certifcate

  - by eskoba

  I am trying to sign certificate (X509) using secret sharing. that is shareholders combine their signatures to produce the final signature. which will be in this case the signed certificate. however practically from my understanding only one entity can sign a certificate. therefore I want to know: which entities or data of the x509certificate are actually taken as input to the signing algorithm? ideally I want this data to be signed by the shareholders and then the final combination will be passed to the X509certificate as valid signature. is this possible? how could it done? if not are they other alternatives?

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• matlab fit exp2

  - by HelloWorld

  I'm unsuccessfully looking for documentation of fit function using exp2 (sum of 2 exponents). How to operate the function is clear: [curve, gof] = fit(x, y,'exp2'); But since there are multiple ways to fit a sum of exponents I'm trying to find out what algorithm is used. Particularly what happens when I'm fitting one exponent (the raw data) with a bit of noise, how the exponents are spread. I've simulated several cases, and it seems that it "drops" all the weight on the second set of coefficients, but row data analysis often shows different behavior. Does anyone have suggestions of documentation?

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• Any tips of how to handle hierarchical trees in relational model?

  - by George

  Hello all. I have a tree structure that can be n-levels deep, without restriction. That means that each node can have another n nodes. What is the best way to retrieve a tree like that without issuing thousands of queries to the database? I looked at a few other models, like flat table model, Preorder Tree Traversal Algorithm, and so. Do you guys have any tips or suggestions of how to implement a efficient tree model? My objective in the real end is to have one or two queries that would spit the whole tree for me. With enough processing i can display the tree in dot net, but that would be in client machine, so, not much of a big deal. Thanks for the attention

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• Prevent Method call without Exception using @PreAuthorize Annotation

  - by Chepech

  Hi all. We are using Spring Security 3. We have a custom implementation of PermissionEvaluator that has this complex algorithm to grant or deny access at method level on the application. To do that we add a @PreAuthorize annotation to the method we want to protect (obviously). Everything is fine on that. However the behavior that we are looking for is that if a hasPermission call is denied, the protected method call only needs to be skipped, instead we are getting a 403 error each time that happens. Any ideas how to prevent that? You can find a different explanation of the problem here; AccessDeniedException handling during methodSecurityInterception

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• What does 'salt' refer to in string-to-key (s2k) specifier?

  - by WilliamKF

  What does 'salt' refer to in string-to-key (s2k) specifier? It appears to be a random number generator to shake things up, but I would like to know what 'salt' stands for? For example it is written: 3.6.1.2. Salted S2K This includes a "salt" value in the S2K specifier -- some arbitrary data -- that gets hashed along with the passphrase string, to help prevent dictionary attacks. Octet 0: 0x01 Octet 1: hash algorithm Octets 2-9: 8-octet salt value Salted S2K is exactly like Simple S2K, except that the input to the hash function(s) consists of the 8 octets of salt from the S2K specifier, followed by the passphrase. But salt is not defined, although its meaning seems clear.

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• GA written in Java

  - by EnderMB

  I am attempting to write a Genetic Algorithm based on techniques I had picked up from the book "AI Techniques for Game Programmers" that uses a binary encoding and fitness proportionate selection (also known as roulette wheel selection) on the genes of the population that are randomly generated within the program in a two-dimensional array. I recently came across a piece of pseudocode and have tried to implement it, but have come across some problems with the specifics of what I need to be doing. I've checked a number of books and some open-source code and am still struggling to progress. I understand that I have to get the sum of the total fitness of the population, pick a random number between the sum and zero, then if the number is greater than the parents to overwrite it, but I am struggling with the implementation of these ideas. Any help in the implementation of these ideas would be very much appreciated as my Java is rusty.

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• how to compare/validate sql schema

  - by Ron Harlev

  I'm looking for a way to validate the SQL schema on a production DB after updating an application version. If the application does not match the DB schema version, there should be a way to warn the user and list the changes needed. Is there a tool or a framework (to use programatically) with built-in features to do that? Or is there some simple algorithm to run this comparison? Update: Red gate lists "from $395". Anything free? Or more foolproof than just keeping the version number?

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• Clojure: Avoiding stack overflow in Sieve of Erathosthene?

  - by nixx

  Here's my implementation of Sieve of Erathosthene in Clojure (based on SICP lesson on streams): (defn nats-from [n] (iterate inc n)) (defn divide? [p q] (zero? (rem q p))) (defn sieve [stream] (lazy-seq (cons (first stream) (sieve (remove #(divide? (first stream) %) (rest stream)))))) (def primes (sieve (nats-from 2))) Now, it's all OK when i take first 100 primes: (take 100 primes) But, if i try to take first 1000 primes, program breaks because of stack overflow. I'm wondering if is it possible to change somehow function sieve to become tail-recursive and, still, to preserve "streamnes" of algorithm? Any help???

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• Qt QTextEdit Qt4.2 Valid HTML String

  - by Matthew Hoggan

  I am trying to generate the correct HTML to render to a QTextEdit Using Qt 4.2 on RHEL 5.3. So far my algorithm generates the following html. I am not an expert web developer, but to me this string seems valid. 319:14:27:22: <font color="rgb(255,0,0)" bgcolor="rgb(255,0,0)">Message</font><br> What needs to change to get the colours to render. Currently it just renders as black text on a white background.

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• Simple string encryption in .NET and Javascript

  - by jonathanconway

  I'm developing an ASP.NET MVC application in which I want to encrypt a short string on the server, using C#, and send it to the client-side. Then on the client-side it will be decrypted through Javascript code. Any thoughts on how to implement this? Do you know of a simple encryption algorithm (doesn't have to be bullet-proof secure) that can be easily translated from C# to Javascript or vice-versa? NOTE: I could do this entirely in C# and do the decryption through Ajax, but I'd prefer not to do it this way, as I want to reduce website traffic as much as possible.

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• Interpolating 1D Gaussian into 2D Gaussian

  - by Drazick

  Let's say I have a 1D Gaussian function. Its length is 600 for that matter. I want to Interpolate it into 2D Gaussian of the size 600 X 600. This is the code I wrote (OTFx is the Gaussian Function, OTF - 2d Interpolated Function): [x, y] = meshgrid([-300:299], [-300:299]); r = sqrt((x .^ 2) + (y .^ 2)); OTF = interp1([-300:299], OTFx, r(:), 'spline'); OTF = reshape(OTF, [600, 600]); The problem is I get Overshoot at the end: How can I prevent it? Is there better Interpolating algorithm for Monotonic Descending Functions?

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• Problem drawing a polygon on data clusters in MATLAB

  - by Hossein

  Hi, I have some data points which I have devided into them into some clusters with some clustering algorithms as the picture below:(it might takes some time for the image to appear) Each color represents different cluster. I have to draw polygons around each cluster. I use convhull for this reason. But as you can see the polygon for the red cluster is very big and covers a lot of areas, which is not the one I am looking for. I need to draw lines(ploygons) exactly around my data sets. For example in the picture above I want a polygon that is drawn exactly the same(and around) as the red cluster with the 3 branches. In other words, in this case I need a polygon with 3 branches to cover my red clusters not that big polygon that covers the whole area. Can anyone help me with this? Please Note that the solution should be general, because the clusters will change in each run of the algorithm, so it needs to be in a way that is general.

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