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• How do I give MacPorts privileges?

  - by cojadate

  I tried to install PostgreSQL server development libraries using MacPorts and got the following: Warning: MacPorts running without privileges. You may be unable to complete certain actions (e.g. install). ---> Computing dependencies for postgresql-server-devel ---> Dependencies to be installed: postgresql-devel ---> Building postgresql-devel Error: Target org.macports.build returned: shell command failed Error: The following dependencies failed to build: postgresql-devel Error: Status 1 encountered during processing. To report a bug, see <http://guide.macports.org/#project.tickets> So I guess that means I need to running MacPorts with privileges and try again. Unfortunately I've no idea how to give MacPorts privileges. I'm running OS X 10.6.3

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• Out of memory error while using clusterdata in MATLAB

  - by Hossein

  Hi, I am trying to cluster a Matrix (size: 20057x2).: T = clusterdata(X,cutoff); but I get this error: ??? Error using == pdistmex Out of memory. Type HELP MEMORY for your options. Error in == pdist at 211 Y = pdistmex(X',dist,additionalArg); Error in == linkage at 139 Z = linkagemex(Y,method,pdistArg); Error in == clusterdata at 88 Z = linkage(X,linkageargs{1},pdistargs); Error in == kmeansTest at 2 T = clusterdata(X,1); can someone help me. I have 4GB of ram, but think that the problem is from somewhere else..

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• Precompile Lambda Expression Tree conversions as constants?

  - by Nathan

  It is fairly common to take an Expression tree, and convert it to some other form, such as a string representation (for example this question and this question, and I suspect Linq2Sql does something similar). In many cases, perhaps even most cases, the Expression tree conversion will always be the same, i.e. if I have a function public string GenerateSomeSql(Expression<Func<TResult, TProperty>> expression) then any call with the same argument will always return the same result for example: GenerateSomeSql(x => x.Age) //suppose this will always return "select Age from Person" GenerateSomeSql(x => x.Ssn) //suppose this will always return "select Ssn from Person" So, in essence, the function call with a particular argument is really just a constant, except time is wasted at runtime re-computing it continuously. Assuming, for the sake of argument, that the conversion was sufficiently complex to cause a noticeable performance hit, is there any way to pre-compile the function call into an actual constant?

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• Getting clusters of rows close together in time

  - by Mike

  I have a table basically like so ID | ItemID | Start | End | --------------------------------------------------------------- 1 234 10/20/09 8:34:22 10/20/09 8:35:10 2 274 10/20/09 8:35:30 10/20/09 8:36:27 3 272 10/21/09 12:15:00 10/21/09 12:17:00 4 112 10/21/09 12:20:14 10/21/09 12:21:21 5 15 10/21/09 12:22:39 10/21/09 12:24:15 There are two "clusters" of entries here, 1-2 and 3-5 separated by a gap in time, specifically 30 minutes is what I'm interested in. What I would like is the first and last rows of the cluster of entries. This is fairly easy to achieve by retrieving all the rows and looping through them in order of start time, but I'd like to have it in SQL if possible. I'm using SQL Server 2008, thanks.

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• Formatting a barcode with hyphens in between - Assignment question

  - by capex

  Hi, The assignment at my first year uni computing course says my program should read a barcode number, and then display the same 13 digit barcode number separated by hyphens. For example, 9300675016902 should look like 930-067501-690-1. The restrictions say I can't use the following: No arrays No strings No functions. Any directions on this? (So far I have done this: part1 = barcode/10000000000; which gives me the first three digits, and this: part4 = barcode%10; which gives me the last digit. Thanks in advance!

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• Sum of path products in DAG

  - by Jules

  Suppose we have a DAG with edges labeled with numbers. Define the value of a path as the product of the labels. For each (source,sink)-pair I want to find the sum of the values of all the paths from source to sink. You can do this in polynomial time with dynamic programming, but there are still some choices that can be made in how you decompose the problem. In my case I have one DAG that has to be evaluated repeatedly with different labelings. My question is: for a given DAG, how can we pre-compute a good strategy for computing these values for different labelings repeatedly. It would be nice if there was an algorithm that finds an optimal way, for example a way that minimizes the number of multiplications. But perhaps this is too much to ask, I would be very happy with an algorithm that just gives a good decomposition.

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• Unable to run OpenMPI across more than two machines

  - by rcollyer

  When attempting to run the first example in the boost::mpi tutorial, I was unable to run across more than two machines. Specifically, this seemed to run fine: mpirun -hostfile hostnames -np 4 boost1 with each hostname in hostnames as <node_name> slots=2 max_slots=2. But, when I increase the number of processes to 5, it just hangs. I have decreased the number of slots/max_slots to 1 with the same result when I exceed 2 machines. On the nodes, this shows up in the job list: <user> Ss orted --daemonize -mca ess env -mca orte_ess_jobid 388497408 \ -mca orte_ess_vpid 2 -mca orte_ess_num_procs 3 -hnp-uri \ 388497408.0;tcp://<node_ip>:48823 Additionally, when I kill it, I get this message: node2- daemon did not report back when launched node3- daemon did not report back when launched The cluster is set up with the mpi and boost libs accessible on an NFS mounted drive. Am I running into a deadlock with NFS? Or, is something else going on?

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• Estimate serialization size of objects?

  - by Stefan K.

  In my thesis, I woud like to enhance messaging in a cluster. It's important to log runtime information about how big a message is (should I prefer processing local or remote). I could just find frameoworks about estimating the object memory size based on java instrumentation. I've tested classmexer, which didn't come close to the serialization size and sourceforge SizeOf. In a small testcase, SizeOf was around 10% wrong and 10x faster than serialization. (Still transient breaks the estimation completely and since e.g. ArrayList is transient but is serialized as an Array, it's not easy to patch SizeOf. But I could live with that) On the other hand, 10x faster with 10% error doesn't seem very good. Any ideas how I could do better?

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• infoWindow on MarkerClusterer

  - by vishwanath

  I need infoWindow to be opened instead of zooming in map, when clicking on the ClusterMarker. I am using Gmaps util library MarkerClusterer for creating cluster of markers. I tried changing following line in markerclusterer.js ClusterMarker_.prototype = new GOverlay(); with ClusterMarker_.prototype = new GMarker(); so that I can get the openInfoWindow() function in the clustermarker, but that didnt worked out. Got some error. If possible, Please suggest solution so that this can be done with MarkerClusterer. Or else any other library which will be able to do this. Any help will be appreciated.

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• Help using Horner's rule and Hash Functions in JAVA?

  - by Matt

  I am trying to use Horner's rule to convert words to integers. I understand how it works and how if the word is long, it may cause an overflow. My ultimate goal is to use the converted integer in a hash function h(x)=x mod tableSize. My book suggests, because of the overflow, you could "apply the mod operator after computing each parenthesized expression in Horner's rule." I don't exactly understand what they mean by this. Say the expression looks like this: ((14*32+15)*32+20)*32+5 Do I take the mod tableSize after each parenthesized expression and add them together? What would it look like with this hash function and this example of Horner's rule?

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• Does anyone know a better alternative to MS Excel's Solver?

  - by tundal45

  My company has to crunch a lot of data and part of the process involves running the solver and plotting a graph through resulting data points. Obviously there is a lot of copy and paste involved and the whole process is shaky, error prone and all round cluster-fudge. I was wondering if there was an alternative to the solver that can be used so that even if we have to use excel to plot the final graph, there will be a lot less data that needs to be copied and pasted back and forth. It would be great especially if the tool could be easily integrated into a .NET application but I am open to suggestions that may require a little bit of code-fu to get this to work. Thanks!

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• Parallelism in Python

  - by fmark

  What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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• Windows/.NET Load Distribution & Balancing

  - by andrewbadera

  Hi all, Is there a vetted Windows-friendly, or even .NET-native, load-distributing/load-balancing utility out there along the lines of HA Proxy? We have a .NET stack product, and the one piece that we step out of the stack is for load-balancing. We need something with configurable rules for distribution -- perhaps subdomain-driven -- that NLB alone doesn't seem to offer. If it integrates directly with .NET, or offers an exposed API callable by webservices, so much the better! Thanks in advance! Clarification: we need to logically part over boxes. This is not just a cluster/failover/replication scenario.

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• Binomial test in Python

  - by Morlock

  I need to do a binomial test in Python that allows calculation for 'n' numbers of the order of 10000. I have implemented a quick binomial_test function using scipy.misc.comb, however, it is pretty much limited around n = 1000, I guess because it reaches the biggest representable number while computing factorials or the combinatorial itself. Here is my function: from scipy.misc import comb def binomial_test(n, k): """Calculate binomial probability """ p = comb(n, k) * 0.5**k * 0.5**(n-k) return p How could I use a native python (or numpy, scipy...) function in order to calculate that binomial probability? If possible, I need scipy 0.7.2 compatible code. Many thanks!

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• Need details about applications that are running on Windows Azure

  - by veda

  I have an application which requires large amount of data storage (say some PB) and computing resources. Instead of going for clusters, I am planning to propose to use Windows Azure Cloud for this application. I have gone through white papers of Windows Azure and have collected some details about Azure. But I feel that is not substantial. I need to do some case study about applications that are running on the azure and that uses azure storage efficiently. I looked for several research paper in related to performance of the applications in Windows Azure. But as Azure was quite new, I wasn't able to find any. Now, I am looking for some white papers/details regarding application that uses azure storage to substantiate my proposal. I also need to understand the windows azure storage architecture and virtual machine architecture. Do anyone know some research papers or details or blogs or something related to these topics.

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• Hadoop on Amazon EC2 : Job tracker not starting properly

  - by Algorist

  Hi, We are running Hadoop on Amazon EC2 cluster. We start the master, slaves and attach the ebs volumes and finally waiting for hadoop jobtracker, tasktracker etc to start and we have timeout of 3600 seconds. We are noticing 50% of the time that job tracker is not able to start before the timeout. Reason being, hdfs is not initialized properly and still in safemode and job tracker is unable to start. I noticed few connectivity issues between nodes on EC2 as I tried manually pinging slaves. Did anyone face similar issue and know how to solve this? Thank you Bala

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• Clojure / HBase: How to Import HBaseTestingUtility in v0.94.6.1

  - by David Williams

  In Clojure, if I want to start a test cluster using the hbase testing utility, I have to annotate my dependencies with: [org.apache.hbase/hbase "0.92.2" :classifier "tests" :scope "test"] First of all, I have no idea what this means. According to leiningens sample project.clj ;; Dependencies are listed as [group-id/name version]; in addition ;; to keywords supported by Pomegranate, you can use :native-prefix ;; to specify a prefix. This prefix is used to extract natives in ;; jars that don't adhere to the default "<os>/<arch>/" layout that ;; Leiningen expects. Question 1: What does that mean? Question 2: If I upgrade the version: [org.apache.hbase/hbase "0.94.6.1" :classifier "tests" :scope "test"] Then I receive a ClassNotFoundException Exception in thread "main" java.lang.ClassNotFoundException: org.apache.hadoop.hbase.HBaseConfiguration Whats going on here and how do I fix it?

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• In C#, can I hide/modify accessors in subclasses?

  - by Diego

  I'm not even sure what this principle is called or how to search for it, so I sincerely apologize if it has been brought up before, but the best way to do it is with an example. class Properties { public string Name { get; set; } } class MyClass { class SubProperties: Properties { public override Name { get { return GetActualName(); } set { _value = SetActualName(value); } } } public SubProperties ClassProperties; private GetActualName() { ClassProperties.Name = "name"; } private SetActualName(string s) { ClassProperties.Name = SomeOtherFunction(s); } } The idea is to have any object that instantiates MyClass have a fully accessible property ClassProperties. To that object, it would look exactly like a Properties object, but behind the scenes, MyClass is actually computing and modifying the results of the fields. This method of declaration is obviously wrong since I can't access GetActualName() and SetActualName() from within the SubProperties definition. How would I achieve something like this?

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• java.io.IOException: Invalid argument

  - by Luixv

  Hi I have a web application running in cluster mode with a load balancer. It consists in two tomcats (T1, and T2) addressing only one DB. T2 is nfs mounted to T1. This is the only dofference between both nodes. I have a java method generating some files. If the request runs on T1 there is no problem but if the request is running on node 2 I get an exception as follows: java.io.IOException: Invalid argument at java.io.FileOutputStream.close0(Native Method) at java.io.FileOutputStream.close(FileOutputStream.java:279) The corresponding code is as follows: for (int i = 0; i < dataFileList.size(); i++) { outputFileName = outputFolder + fileNameList.get(i); FileOutputStream fileOut = new FileOutputStream(outputFileName); fileOut.write(dataFileList.get(i), 0, dataFileList.get(i).length); fileOut.flush(); fileOut.close(); } The exception appears at the fileOut.close() Any hint? Luis

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• C or Ada for engineering computations?

  - by yCalleecharan

  Hi,as an engineer I currently use C to write programs dealing with numerical methods. I like C as it's very fast. I don't want to move to C++ and I have been reading a bit about Ada which has some very good sides. I believe that much of the software in big industries have been or more correctly were written in Ada. I would like to know how C compares with Ada. Is Ada fast as C? I understand that no language is perfect but I would like to know if Ada was designed for scientific computing. Thanks a lot...

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• Scripting window positioning in OS X

  - by Matt Trent

  My primary computing setup is a macbook pro with a large external monitor. I'm looking for a convenient way of moving a number of the windows of open programs from the laptop screen to the external monitor when I plug it in. I've seen a few partial scripts for accomplishing this, but nothing comprehensive. Ideally I'd like to specify the laptop screen location and external monitor location for each window and be able to toggle between them. Is anyone aware of any existing utility or Applscripts that can perform this?

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• DynaCache invalidation in clustered environment

  - by Ravi

  We are using Horizontal cluster in our PROD with WAS 6.1 as the Application server. We have enabled dynacache service for some of the JSP fragments using SHARED-PUSH in cachespec.xml file. Now we want to do cache invalidation programmatically..ie. whenever something changes in DB related to cache the cache should get invalidated. so can you please let me know what steps are involved in it to achieve this? any configuration settings at server side or any development changes.

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• Efficiency of while(true) ServerSocket Listen

  - by Submerged

  I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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• What's the coolest machine you've ever worked on?

  - by mxg

  What's the most exotic, coolest, unique, or interesting machine you've worked on? Most of us work on machines with x86 architectures using some Windows or Linux variant. I'm sure there are those of you out there who are working on or have worked on machines with experimental architecures, or operating systems. Maybe you worked on a machine that has some sigificance in the history of computing. I'd be interested to hear about it. I'm sure others reading SO will as well. EDIT: I appreciate all of you who took some time to talk about their experiences with interesting or unusual machines. I enjoyed reading your answers. Although it wasn't my intent to get nostalgic, I see that theme amongst the responses.

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• Semantic stuff (RDF, OWL) on mobile phones - is it possible?

  - by Brian Schimmel

  I'm thinking about using semantic (web) technogies like RDF and OWL in an application on mobile devices. Currently I'm targeting android, but I'd also be interested in the possibilities on the iPhone and on J2ME. I would like to use a lib instead of implementing everything from scratch. I know that there are some libraries and frameworks like Jena, Redland, Protégé but they don't state on which platforms they are known to work. Having a dynamic object model and parsing from and to XML are must-haves for me. I'd also like to use reasoning, but I've been told it was rather computing-intensive, so that's only a nice-to-have. For all platforms mentioned, the question can be interpreted as Is it possible in theory (especially for J2ME I'm not sure) Are there libs that are known to work on those platforms? Is the performance on a mobile platform good enough for real world usage?

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