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• strsplit in R with metacharacter

  - by user1429852

  I have received a large amount of data where the delimiter is a backslash (obviously a bad choice). I'm processing it in R for computation, and having a hard time finding how to split the string since the backslash is a metacharacter. For example, a string would look like this: "1128\0019\XA5\E2R\366\00=15" and I want to split it along the "\" character, but when I run the strsplit command: strsplit(tempStr, "\") Error in strsplit(tempStr, "\") : invalid regular expression '\', reason 'Trailing backslash' When I try to used the "fixed" option, it does not run because it is expecting something after the backslash: strsplit(tempStr, "\", fixed = TRUE) Unfortunately, I can't preprocess the data with another program because the data is generated daily. Please help and thanks!

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• How to speed this kind of for-loop?

  - by wok

  I would like to compute the maximum of translated images along the direction of a given axis. I know about ordfilt2, however I would like to avoid using the Image Processing Toolbox. So here is the code I have so far: imInput = imread('tire.tif'); n = 10; imMax = imInput(:, n:end); for i = 1:(n-1) imMax = max(imMax, imInput(:, i:end-(n-i))); end Is it possible to avoid using a for-loop in order to speed the computation up, and, if so, how?

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• Speedup C++ code

  - by Werner

  Hi, I am writing a C++ number crunching application, where the bottleneck is a function that has to calculate for double: template<class T> inline T sqr(const T& x){return x*x;} and another one that calculates Base dist2(const Point& p) const { return sqr(x-p.x) + sqr(y-p.y) + sqr(z-p.z); } These operations take 80% of the computation time. I wonder if you can suggest approaches to make it faster, even if there is some sort of accuracy loss Thanks

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• Is there a way to force CoreImage to use the GPU?

  - by NSSplendid

  We are having the following problem: a series of Core Image filters runs constantly in our program. When evaluating on my Macbook Pro, Core Image decides to schedule all graphics computation on the GPU, as expected. When using a MacPro, however, CI uses the CPUs! This is a problem, as we need them for other processing. [1] The question now is: Can one tell CI to run exclusively on the GPU? [1] Both hardware sets are of the newest kind. The MacPro has 8 Cores.

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• Minimizing calls to database in rails

  - by ming yeow

  Hi guys, i am familiar with memcached and eager loading, but neither seems to solve the problem i am facing. My main performance lag comes from hundreds of data retrieval calls from the database. The tricky thing is that I do not know which set of users i need to retrieve until i have several steps of computation. I can refactor my code, but i was wondering how you experts handle this situation? I think it should be a fairly common situation def newsfeed - find out which users i need - retrieve those users via DB - find out which events happened for these users - for each of those events - retrieve new set of users - find out which groups are relevant - for each of those groups - retrieve new set of users - etc, etc end

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• Twin edges - Half edge data structure

  - by Pradeep Kumar

  I have implemented a Half-edge data structure for loading 3d objects. I find that the part of assigning twin/pair edges takes the longest computation time (especially for objects which have hundreds of thousands half edges). The reason is that I use nested loops to accomplish this. Is there a simpler and efficient way of doing this? Below is the code which I've written. HE is the half-edge data structure. hearr is a vector containing all the half edges. vert is the starting vertex and end is the ending vertex. Thanks!! HE *e1,*e2; for(size_t i=0;i<hearr.size();i++){ e1=hearr[i]; for(size_t j=1;j<hearr.size();j++){ e2=hearr[j]; if((e1->vert==e2->end)&&(e2->vert==e1->end)){ e1->twin=e2; e2->twin=e1; } } }

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• Mathematica Programming Language&ndash;An Introduction

  - by JoshReuben

  The Mathematica http://www.wolfram.com/mathematica/ programming model consists of a kernel computation engine (or grid of such engines) and a front-end of notebook instances that communicate with the kernel throughout a session. The programming model of Mathematica is incredibly rich & powerful – besides numeric calculations, it supports symbols (eg Pi, I, E) and control flow logic.   obviously I could use this as a simple calculator: 5 * 10 --> 50 but this language is much more than that!   for example, I could use control flow logic & setup a simple infinite loop: x=1; While [x>0, x=x,x+1] Different brackets have different purposes: square brackets for function arguments:  Cos[x] round brackets for grouping: (1+2)*3 curly brackets for lists: {1,2,3,4} The power of Mathematica (as opposed to say Matlab) is that it gives exact symbolic answers instead of a rounded numeric approximation (unless you request it):   Mathematica lets you define scoped variables (symbols): a=1; b=2; c=a+b --> 5 these variables can contain symbolic values – you can think of these as partially computed functions:   use Clear[x] or Remove[x] to zero or dereference a variable.   To compute a numerical approximation to n significant digits (default n=6), use N[x,n] or the //N prefix: Pi //N -->3.14159 N[Pi,50] --> 3.1415926535897932384626433832795028841971693993751 The kernel uses % to reference the lastcalculation result, %% the 2nd last, %%% the 3rd last etc –> clearer statements: eg instead of: Sqrt[Pi+Sqrt[Sqrt[Pi+Sqrt[Pi]]] do: Sqrt[Pi]; Sqrt[Pi+%]; Sqrt[Pi+%] The help system supports wildcards, so I can search for functions like so: ?Inv* Mathematica supports some very powerful programming constructs and a rich function library that allow you to do things that you would have to write allot of code for in a language like C++.   the Factor function – factorization: Factor[x^3 – 6*x^2 +11x – 6] --> (-3+x) (-2+x) (-1+x)   the Solve function – find the roots of an equation: Solve[x^3 – 2x + 1 == 0] -->   the Expand function – express (1+x)^10 in polynomial form: Expand[(1+x)^10] --> 1+10x+45x^2+120x^3+210x^4+252x^5+210x^6+120x^7+45x^8+10x^9+x^10 the Prime function – what is the 1000th prime? Prime[1000] -->7919 Mathematica also has some powerful graphics capabilities:   the Plot function – plot the graph of y=Sin x in a single period: Plot[Sin[x], {x,0,2*Pi}] you can also plot 3D surfaces of functions using Plot3D function

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• JavaScript in different browsers

  - by PointsToShare

  Adventures with JavaScript rendered in IE 8, Chrome 15, and Firefox 8.0 I have written a little monogram about the advantages of Math and wrote a few JavaScript applications to demonstrate them. I was a bit careless and used elements on the page in my JavaScript without using any of the GetElementsByXXXX methods to identify them.  Say I had a text box named tbSeqNum into which I entered a number to be used in a computation. In my code I simply referred to its value by using it directly. Like here: Function Blah() {                 return tbSeqNum.value; } This ran fine in IE8. In IE, the elements are available as global variables. This is not the case in either Firefox or Chrome. In there one has to create the variable and only then use it. Assuming I also used tbSeqNum as the element’s ID, this works: Function Blah() {                 return GetElementById(“tbSeqNum”).value; } Naturally this corrected function also works in IE, so be warned. Also, coming from windows programming (I am long in the tooth and programmed long before the internet), I have a habit of putting an “Exit” button on my pages and setting their onclick to: onclick=”window.close()”. Again, this works fine in IE. In Firefox and chrome, it does not! There you can only close a window that you opened in the code. A window that was opened by navigation to a URL will not close.  Before I deployed mu code to my website, I painfully removed all my Exit buttons. But my greatest surprise came when I tested my pages in the various browsers. In my code I do a comparison on the performance of two algorithms used to solve the same problem. One is brute force, the other uses a mathematical formula. The compare functions runs each many times and displays the time it took for each and also the ratio. Chrome runs JavaScript between 5 and 10 times faster than Firefox and between 50 and 100 times faster that IE. Wow!!! This difference is especially remarkable when the code uses iteration. I suspect that the JS engines in Chrome and Firefox simply cache the result of a function and if it is called again with the same parameters, it returns the cached result. To see it in action play run the “How Many Squares” page in www.mgsltns.com/games.htm The host is running on Unix, so the link is case sensitive. Last Note: IE9 runs JS a bit faster, but still lags behind almost as badly. That’s All Folks!

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• OpenGL flickerinng near the edges

  - by Daniel

  I am trying to simulate particles moving around the scene with OpenCL for computation and OpenGL for rendering with GLUT. There is no OpenCL-OpenGL interop yet, so the drawing is done in the older fixed pipeline way. Whenever circles get close to the edges, they start to flicker. The drawing should draw a part of the circle on the top of the scene and a part on the bottom. The effect is the following: The balls you see on the bottom should be one part on the bottom and one part on the top. Wrapping around the scene, so to say, but they constantly flicker. The code for drawing them is: void Scene::drawCircle(GLuint index){ glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef(pos.at(2*index),pos.at(2*index+1), 0.0f); glBegin(GL_TRIANGLE_FAN); GLfloat incr = (2.0 * M_PI) / (GLfloat) slices; glColor3f(0.8f, 0.255f, 0.26f); glVertex2f(0.0f, 0.0f); glColor3f(1.0f, 0.0f, 0.0f); for(GLint i = 0; i <=slices; ++i){ GLfloat x = radius * sin((GLfloat) i * incr); GLfloat y = radius * cos((GLfloat) i * incr); glVertex2f(x, y); } glEnd(); } If it helps, this is the reshape method: void Scene::reshape(GLint width, GLint height){ if(0 == height) height = 1; //Prevent division by zero glViewport(0, 0, width, height); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluOrtho2D(xmin, xmax, ymin, ymax); std::cout << xmin << " " << xmax << " " << ymin << " " << ymax << std::endl; }

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• Suggestions for getting an open source electron beam tracking code going

  - by Boaz

  I work in the field of accelerator physics and synchrotron radiation. High energy electrons circulating in large rings of magnets produce x-rays that are used for a variety of different kinds of science. Running and improving these facilities requires controlling and modelling the electron beam as it circulates in the ring. A code to model this basically requires trackers to follow the electrons through the elements (something called a symplectic integrator), and then the computation of different parameters associated with this motion. The problem with these codes is that every facility has there own. In principle the code is not so complex. And as a modelling project, one might think it has some general interest. Who doesn't want to be able to create a track in space out of magnets and watch the electrons circulate? There is a Matlab based code to do this called Accelerator Toolbox, but the creator of the code is no longer in the field. I put the code in Sourceforge under the name atcollab. The basic resource is in C- it is the set of symplectic integrators. These are available in the atcollab code here. It has been useful to put the code on Sourceforge in order to exchange code, but the community of users is quite small and most are too busy to put that much time into collaboration. So in terms of really improving the code, I don't think it has been so successful. Any piece of this picture could be recreated without that much difficulty, but overall it is a bit complex, and because each lab has their own installation with lots of add-on Matlab code, people find it hard to really work together and share code. Somehow I think we need to involve a wider community in our development, or just use some standard tools. But for that, I suppose it needs to be of some general interest. I think symplectic integrators may have some general interest. And the part about a plug-in architecture to build up the ring ought to fit other patterns. Or the other option is to just accept that this is not a problem of general interest, and work harder within our small community. Suggestions, or anecdotes of analogous experience would be appreciated.

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• How to remove the boundary effects arising due to zero padding in scipy/numpy fft?

  - by Omkar

  I have made a python code to smoothen a given signal using the Weierstrass transform, which is basically the convolution of a normalised gaussian with a signal. The code is as follows: #Importing relevant libraries from __future__ import division from scipy.signal import fftconvolve import numpy as np def smooth_func(sig, x, t= 0.002): N = len(x) x1 = x[-1] x0 = x[0] # defining a new array y which is symmetric around zero, to make the gaussian symmetric. y = np.linspace(-(x1-x0)/2, (x1-x0)/2, N) #gaussian centered around zero. gaus = np.exp(-y**(2)/t) #using fftconvolve to speed up the convolution; gaus.sum() is the normalization constant. return fftconvolve(sig, gaus/gaus.sum(), mode='same') If I run this code for say a step function, it smoothens the corner, but at the boundary it interprets another corner and smoothens that too, as a result giving unnecessary behaviour at the boundary. I explain this with a figure shown in the link below. Boundary effects This problem does not arise if we directly integrate to find convolution. Hence the problem is not in Weierstrass transform, and hence the problem is in the fftconvolve function of scipy. To understand why this problem arises we first need to understand the working of fftconvolve in scipy. The fftconvolve function basically uses the convolution theorem to speed up the computation. In short it says: convolution(int1,int2)=ifft(fft(int1)*fft(int2)) If we directly apply this theorem we dont get the desired result. To get the desired result we need to take the fft on a array double the size of max(int1,int2). But this leads to the undesired boundary effects. This is because in the fft code, if size(int) is greater than the size(over which to take fft) it zero pads the input and then takes the fft. This zero padding is exactly what is responsible for the undesired boundary effects. Can you suggest a way to remove this boundary effects? I have tried to remove it by a simple trick. After smoothening the function I am compairing the value of the smoothened signal with the original signal near the boundaries and if they dont match I replace the value of the smoothened func with the input signal at that point. It is as follows: i = 0 eps=1e-3 while abs(smooth[i]-sig[i])> eps: #compairing the signals on the left boundary smooth[i] = sig[i] i = i + 1 j = -1 while abs(smooth[j]-sig[j])> eps: # compairing on the right boundary. smooth[j] = sig[j] j = j - 1 There is a problem with this method, because of using an epsilon there are small jumps in the smoothened function, as shown below: jumps in the smooth func Can there be any changes made in the above method to solve this boundary problem?

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• Why is multithreading often preferred for improving performance?

  - by user1849534

  I have a question, it's about why programmers seems to love concurrency and multi-threaded programs in general. I'm considering 2 main approaches here: an async approach basically based on signals, or just an async approach as called by many papers and languages like the new C# 5.0 for example, and a "companion thread" that manages the policy of your pipeline a concurrent approach or multi-threading approach I will just say that I'm thinking about the hardware here and the worst case scenario, and I have tested this 2 paradigms myself, the async paradigm is a winner at the point that I don't get why people 90% of the time talk about multi-threading when they want to speed up things or make a good use of their resources. I have tested multi-threaded programs and async program on an old machine with an Intel quad-core that doesn't offer a memory controller inside the CPU, the memory is managed entirely by the motherboard, well in this case performances are horrible with a multi-threaded application, even a relatively low number of threads like 3-4-5 can be a problem, the application is unresponsive and is just slow and unpleasant. A good async approach is, on the other hand, probably not faster but it's not worst either, my application just waits for the result and doesn't hangs, it's responsive and there is a much better scaling going on. I have also discovered that a context change in the threading world it's not that cheap in real world scenario, it's in fact quite expensive especially when you have more than 2 threads that need to cycle and swap among each other to be computed. On modern CPUs the situation it's not really that different, the memory controller it's integrated but my point is that an x86 CPUs is basically a serial machine and the memory controller works the same way as with the old machine with an external memory controller on the motherboard. The context switch is still a relevant cost in my application and the fact that the memory controller it's integrated or that the newer CPU have more than 2 core it's not bargain for me. For what i have experienced the concurrent approach is good in theory but not that good in practice, with the memory model imposed by the hardware, it's hard to make a good use of this paradigm, also it introduces a lot of issues ranging from the use of my data structures to the join of multiple threads. Also both paradigms do not offer any security abut when the task or the job will be done in a certain point in time, making them really similar from a functional point of view. According to the X86 memory model, why the majority of people suggest to use concurrency with C++ and not just an async approach ? Also why not considering the worst case scenario of a computer where the context switch is probably more expensive than the computation itself ?

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• "Hello World" in C++ AMP

  - by Daniel Moth

  Some say that the equivalent of "hello world" code in the data parallel world is matrix multiplication :) Below is the before C++ AMP and after C++ AMP code. For more on what it all means, watch the recording of my C++ AMP introduction (the example below is part of the session). void MatrixMultiply(vector<float>& vC, const vector<float>& vA, const vector<float>& vB, int M, int N, int W ) { for (int y = 0; y < M; y++) { for (int x = 0; x < N; x++) { float sum = 0; for(int i = 0; i < W; i++) { sum += vA[y * W + i] * vB[i * N + x]; } vC[y * N + x] = sum; } } } Change the function to use C++ AMP and hence offload the computation to the GPU, and now the calling code (which I am not showing) needs no changes and the overall operation gives you really nice speed up for large datasets…  #include <amp.h> using namespace concurrency; void MatrixMultiply(vector<float>& vC, const vector<float>& vA, const vector<float>& vB, int M, int N, int W ) { array_view<const float,2> a(M, W, vA); array_view<const float,2> b(W, N, vB); array_view<writeonly<float>,2> c(M, N, vC); parallel_for_each( c.grid, [=](index<2> idx) mutable restrict(direct3d) { float sum = 0; for(int i = 0; i < a.x; i++) { sum += a(idx.y, i) * b(i, idx.x); } c[idx] = sum; } ); } Again, you can understand the elements above, by using my C++ AMP presentation slides and recording… Stay tuned for more… Comments about this post welcome at the original blog.

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• Are closures with side-effects considered "functional style"?

  - by Giorgio

  Many modern programming languages support some concept of closure, i.e. of a piece of code (a block or a function) that Can be treated as a value, and therefore stored in a variable, passed around to different parts of the code, be defined in one part of a program and invoked in a totally different part of the same program. Can capture variables from the context in which it is defined, and access them when it is later invoked (possibly in a totally different context). Here is an example of a closure written in Scala: def filterList(xs: List[Int], lowerBound: Int): List[Int] = xs.filter(x => x >= lowerBound) The function literal x => x >= lowerBound contains the free variable lowerBound, which is closed (bound) by the argument of the function filterList that has the same name. The closure is passed to the library method filter, which can invoke it repeatedly as a normal function. I have been reading a lot of questions and answers on this site and, as far as I understand, the term closure is often automatically associated with functional programming and functional programming style. The definition of function programming on wikipedia reads: In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast to the imperative programming style, which emphasizes changes in state. and further on [...] in functional code, the output value of a function depends only on the arguments that are input to the function [...]. Eliminating side effects can make it much easier to understand and predict the behavior of a program, which is one of the key motivations for the development of functional programming. On the other hand, many closure constructs provided by programming languages allow a closure to capture non-local variables and change them when the closure is invoked, thus producing a side effect on the environment in which they were defined. In this case, closures implement the first idea of functional programming (functions are first-class entities that can be moved around like other values) but neglect the second idea (avoiding side-effects). Is this use of closures with side effects considered functional style or are closures considered a more general construct that can be used both for a functional and a non-functional programming style? Is there any literature on this topic? IMPORTANT NOTE I am not questioning the usefulness of side-effects or of having closures with side effects. Also, I am not interested in a discussion about the advantages / disadvantages of closures with or without side effects. I am only interested to know if using such closures is still considered functional style by the proponent of functional programming or if, on the contrary, their use is discouraged when using a functional style.

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• Is return-type-(only)-polymorphism in Haskell a good thing?

  - by dainichi

  One thing that I've never quite come to terms with in Haskell is how you can have polymorphic constants and functions whose return type cannot be determined by their input type, like class Foo a where foo::Int -> a Some of the reasons that I do not like this: Referential transparency: "In Haskell, given the same input, a function will always return the same output", but is that really true? read "3" return 3 when used in an Int context, but throws an error when used in a, say, (Int,Int) context. Yes, you can argue that read is also taking a type parameter, but the implicitness of the type parameter makes it lose some of its beauty in my opinion. Monomorphism restriction: One of the most annoying things about Haskell. Correct me if I'm wrong, but the whole reason for the MR is that computation that looks shared might not be because the type parameter is implicit. Type defaulting: Again one of the most annoying things about Haskell. Happens e.g. if you pass the result of functions polymorphic in their output to functions polymorphic in their input. Again, correct me if I'm wrong, but this would not be necessary without functions whose return type cannot be determined by their input type (and polymorphic constants). So my question is (running the risk of being stamped as a "discussion quesion"): Would it be possible to create a Haskell-like language where the type checker disallows these kinds of definitions? If so, what would be the benefits/disadvantages of that restriction? I can see some immediate problems: If, say, 2 only had the type Integer, 2/3 wouldn't type check anymore with the current definition of /. But in this case, I think type classes with functional dependencies could come to the rescue (yes, I know that this is an extension). Furthermore, I think it is a lot more intuitive to have functions that can take different input types, than to have functions that are restricted in their input types, but we just pass polymorphic values to them. The typing of values like [] and Nothing seems to me like a tougher nut to crack. I haven't thought of a good way to handle them. I doubt I am the first person to have had thoughts like these. Does anybody have links to good discussions about this Haskell design decision and the pros/cons of it?

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• Does OO, TDD, and Refactoring to Smaller Functions affect Speed of Code?

  - by Dennis

  In Computer Science field, I have noticed a notable shift in thinking when it comes to programming. The advice as it stands now is write smaller, more testable code refactor existing code into smaller and smaller chunks of code until most of your methods/functions are just a few lines long write functions that only do one thing (which makes them smaller again) This is a change compared to the "old" or "bad" code practices where you have methods spanning 2500 lines, and big classes doing everything. My question is this: when it call comes down to machine code, to 1s and 0s, to assembly instructions, should I be at all concerned that my class-separated code with variety of small-to-tiny functions generates too much extra overhead? While I am not exactly familiar with how OO code and function calls are handled in ASM in the end, I do have some idea. I assume that each extra function call, object call, or include call (in some languages), generate an extra set of instructions, thereby increasing code's volume and adding various overhead, without adding actual "useful" code. I also imagine that good optimizations can be done to ASM before it is actually ran on the hardware, but that optimization can only do so much too. Hence, my question -- how much overhead (in space and speed) does well-separated code (split up across hundreds of files, classes, and methods) actually introduce compared to having "one big method that contains everything", due to this overhead? UPDATE for clarity: I am assuming that adding more and more functions and more and more objects and classes in a code will result in more and more parameter passing between smaller code pieces. It was said somewhere (quote TBD) that up to 70% of all code is made up of ASM's MOV instruction - loading CPU registers with proper variables, not the actual computation being done. In my case, you load up CPU's time with PUSH/POP instructions to provide linkage and parameter passing between various pieces of code. The smaller you make your pieces of code, the more overhead "linkage" is required. I am concerned that this linkage adds to software bloat and slow-down and I am wondering if I should be concerned about this, and how much, if any at all, because current and future generations of programmers who are building software for the next century, will have to live with and consume software built using these practices. UPDATE: Multiple files I am writing new code now that is slowly replacing old code. In particular I've noted that one of the old classes was a ~3000 line file (as mentioned earlier). Now it is becoming a set of 15-20 files located across various directories, including test files and not including PHP framework I am using to bind some things together. More files are coming as well. When it comes to disk I/O, loading multiple files is slower than loading one large file. Of course not all files are loaded, they are loaded as needed, and disk caching and memory caching options exist, and yet still I believe that loading multiple files takes more processing than loading a single file into memory. I am adding that to my concern.

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• Why C++ people loves multithreading when it comes to performances?

  - by user1849534

  I have a question, it's about why programmers seems to love concurrency and multi-threaded programs in general. I'm considering 2 main approach here: an async approach basically based on signals, or just an async approach as called by many papers and languages like the new C# 5.0 for example, and a "companion thread" that maanges the policy of your pipeline a concurrent approach or multi-threading approach I will just say that I'm thinking about the hardware here and the worst case scenario, and I have tested this 2 paradigms myself, the async paradigm is a winner at the point that I don't get why people 90% of the time talk about concurrency when they wont to speed up things or make a good use of their resources. I have tested multi-threaded programs and async program on an old machine with an Intel quad-core that doesn't offer a memory controller inside the CPU, the memory is managed entirely by the motherboard, well in this case performances are horrible with a multi-threaded application, even a relatively low number of threads like 3-4-5 can be a problem, the application is unresponsive and is just slow and unpleasant. A good async approach is, on the other hand, probably not faster but it's not worst either, my application just waits for the result and doesn't hangs, it's responsive and there is a much better scaling going on. I have also discovered that a context change in the threading world it's not that cheap in real world scenario, it's infact quite expensive especially when you have more than 2 threads that need to cycle and swap among each other to be computed. On modern CPUs the situation it's not really that different, the memory controller it's integrated but my point is that an x86 CPUs is basically a serial machine and the memory controller works the same way as with the old machine with an external memory controller on the motherboard. The context switch is still a relevant cost in my application and the fact that the memory controller it's integrated or that the newer CPU have more than 2 core it's not bargain for me. For what i have experienced the concurrent approach is good in theory but not that good in practice, with the memory model imposed by the hardware, it's hard to make a good use of this paradigm, also it introduces a lot of issues ranging from the use of my data structures to the join of multiple threads. Also both paradigms do not offer any security abut when the task or the job will be done in a certain point in time, making them really similar from a functional point of view. According to the X86 memory model, why the majority of people suggest to use concurrency with C++ and not just an async aproach ? Also why not considering the worst case scenario of a computer where the context switch is probably more expensive than the computation itself ?

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• How do I install an HP home-use printer on Windows Home Server (Windows Server 2003)

  - by Rob Allen

  I have an HP DeskJet F4210 printer that I would like to share on my network via Windows Home Server. Unfortunately, the driver installation checks for supported OS's, detects Home Server as Windows Server 2003 and exits. The driver install supports WinXP, W2k, Vista, and Win98SE. In theory, drivers for XP or Windows 2000 should work fine with Home Server. When using the "Install Printer" tool in Home Server I am only able to select .inf files (there are serveral on the install media) but the driver folders for XP and 2000 have .sys and .dll files. How can I bypass HP's short-sighted install program and get this printer up and running on Home server? I'll be happy with basic print functionality and will save the task of enabling scanning for another time.

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• Always a path to the internet even in Windows SBS is off

  - by Mark

  Hello all, is it possible to have a configuration in a Windows 2003 SBS environment where in the event that the SBS box crashed/turned off/ or is being worked on that there can still exist a path to the internet for domain users and visitors to still use? I would like to have the standalone router issue DHCP IPs. The primary DNS would point to the SBS, the secondary wouuld point to the ISP DNS Server. My theory was that if someone was using the internet and the SBS box went down they wouldn't be able to access the network shares but still be able to use the internet. (We are moving everything into the clouds with Google Apps Non-Profit) Does this seem like a reasonable configuration? Or are they're pitfalls that I will fall into? Thanks Mark

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• USB hard drive doesn't graceful power off after eject on Windows 7

  - by Sim

  I have a couple of Seagate FreeAgent Go external USB hard drives and would like them to gracefully power off after ejecting in Windows 7. With Windows XP a few seconds after they are ejected they gracefully power off. When ejecting them on Windows 7 they just stay on and have to be physically disconnected before they lose power. I have checked the hard drive removal policy and it is set to quick removal. I have also looked in the Seagate forums but I couldn't find any info on this so I thought I'd ask the SuperUser community on any ideas why the difference and how to get the same behaviour in Windows 7 as in XP? Update: I am finding that this also happens with USB thumb drives as well. My current theory is that there were changes to the driver model with Vista/Win 7 that haven't been reflected in the device drivers yet. So things that worked under XP don't under Win7 as the drivers haven't been updated for the new model. Does that sound right?

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• What kind of storage do people actually use for VMware ESX servers?

  - by Dirk Paessler

  VMware and many network evangelists try to tell you that sophisticated (=expensive) fiber SANs are the "only" storage option for VMware ESX and ESXi servers. Well, yes, of course. Using a SAN is fast, reliable and makes vMotion possible. Great. But: Can all ESX/ESXi users really afford SANs? My theory is that less than 20% of all VMware ESX installations on this planet actually use fiber or iSCS SANs. Most of these installation will be in larger companies who can afford this. I would predict that most VMware installations use "attached storage" (vmdks are stored on disks inside the server). Most of them run in SMEs and there are so many of them! We run two ESX 3.5 servers with attached storage and two ESX 4 servers with an iSCS san. And the "real live difference" between both is barely notable :-) Do you know of any official statistics for this question? What do you use as your storage medium?

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• Windows Server 2008, IIS7 and Windows Authentication

  - by Chalkey

  We currently have a development server set up which we are trying to test some Windows authentication ASP.NET code on. We have turned on Windows Authentication in IIS7 on Windows Server 2008 R2 fine, and it asks the user for a username and password as excepted, but the problem is it doesn't appear to accept any credentials. This code for example... Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Page.Title = "Home page for " + User.Identity.Name End Sub ...always returns an empty string. One theory we have is that we dont have Active Directory installed as of yet, we are just testing this by logging on via the machine name not a domain. Is this type of authentication only applicatable to domains (if so we can probably install Active Directory and some test accounts) - or is it possible to get the user identity when logging in using the machine name? Ideally we would like to be able to test this on our local machines (Windows 7 Pro) using our own accounts (again these aren't on a domain) and IIS but this has the same issue as our dev server. Thanks,

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• Is email encryption practical enough?

  - by Dimitri C.

  All emails I have ever sent were sent as plain text. Like postcards, everybody on the way to the addressee could easily read and store them. This worries me. I know privacy is something of the past, but encrypting email is possible, at least in theory. However, I wonder whether it is practical enough. Is there anybody who has experience with email security? Is it easy to set up? And can you still send and receive email from all you friends and acquaintances?

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• Secure PHP environments with PHP-FPM and SFTP

  - by pdd

  I'd like to set up secure environments for a small number of untrusted PHP websites on a Debian server. Right now everything runs on the same Apache2 with mod_php5 and vsftpd for administrative file access, so there is room for improvement. The idea is to use nginx instead of apache, SFTP through OpenSSH instead of vsftpd and chrooted (in sshd_config), individual users for each website with their own pool of PHP processes. All these users and nginx are part of the same group. Now in theory I can set 700 permissions on all PHP scripts and 750 on static files that nginx has to serve up. Theoretically, if a website is compromised all the other users' data is safe, right? Are there better solutions that require less setup time and memory per website? Cheers

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• Windows shutdown processes termination sequence

  - by jpmartins

  I've seen today an wierd situation. I have a theory, but it would help to know more about the windows shutdown process. If you have some knowlaged about it please share. A machine was shutdown (at this moment I suspect an unexpected mantainace), on that machine there was a long running process that was interrupted. Monitorization confirms that the process did not terminated normally. Loking at the logs for the long running process it seem that was just finishing. That seems higly unprobable since it was running for more than 6 hours (witch is a bit more than the usual 5 hours). The process lanches child processes and waits for results from them, I suspect pour error control on the parent process and that the shutdown as terminated child processes before.

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