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  • When is a program limited by the memory bandwidth?

    - by hanno
    I want to know if a program that I am using and which requires a lot of memory is limited by the memory bandwidth. When do you expect this to happen? Did it ever happen to you in a real life scenario? I found several articles discussing this issue, including http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node12.html http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node13.html http://ispass.org/ucas5/session2_3_ibm.pdf The first link is a bit old, but suggests that you need to perform less than about 1-40 floating point operations per floating point variable in order to see this effect (correct me if I'm wrong). How can I measure the memory bandwidth that a given program is using and how do I measure the (peak) bandwidth that my system can offer? I don't want to discuss any complicated cache issues here. I'm only interested in the communication between the CPU and the memory.

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  • Yet another (13)Permission denied error on Apache2 server

    - by lollercoaster
    I just can't figure it out. I'm running apache2 on a Ubuntu 10.04 i386 server. Whenever I visit my server (has an IP address, and is connected to internet with static IP xxx.xxx.xxx.xxx) so that's not the problem) in browser, mysub.domain.edu (renamed here), I get the following: Forbidden You don't have permission to access /index.html on this server The apache2 error log confirms this: [Mon Apr 18 02:38:20 2011] [error] [client zzz.zzz.zzz.zzz] (13)Permission denied: access to / denied I'll try to provide all necessary information below: 1) Contents of /etc/apache2/httpd.conf DirectoryIndex index.html index.php 2) Contents of /etc/apache2/sites-available/default <VirtualHost *:80> ServerAdmin [email protected] DocumentRoot /home/myusername/htdocs <Directory /> Options FollowSymLinks AllowOverride None </Directory> <Directory "/home/myusername/htdocs/"> Options Indexes FollowSymLinks MultiViews AllowOverride None order allow,deny allow from all DirectoryIndex index.html index.php Satisfy any </Directory> ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/ <Directory "/usr/lib/cgi-bin"> AllowOverride None Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch Order allow,deny Allow from all </Directory> ErrorLog /var/log/apache2/error.log # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. LogLevel warn CustomLog /var/log/apache2/access.log combined Alias /doc/ "/usr/share/doc/" <Directory "/usr/share/doc/"> Options Indexes MultiViews FollowSymLinks AllowOverride None Order deny,allow Deny from all Allow from 127.0.0.0/255.0.0.0 ::1/128 </Directory> ServerName mysub.domain.edu </VirtualHost> 3) Contents of /etc/apache2/sites-enabled/000-default <VirtualHost *:80> ServerAdmin [email protected] DocumentRoot /home/myusername/htdocs <Directory /> Options FollowSymLinks AllowOverride None </Directory> <Directory "/home/myusername/htdocs/"> Options Indexes FollowSymLinks MultiViews AllowOverride None order allow,deny allow from all DirectoryIndex index.html index.php Satisfy any </Directory> ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/ <Directory "/usr/lib/cgi-bin"> AllowOverride None Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch Order allow,deny Allow from all </Directory> ErrorLog /var/log/apache2/error.log # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. LogLevel warn CustomLog /var/log/apache2/access.log combined Alias /doc/ "/usr/share/doc/" <Directory "/usr/share/doc/"> Options Indexes MultiViews FollowSymLinks AllowOverride None Order deny,allow Deny from all Allow from 127.0.0.0/255.0.0.0 ::1/128 </Directory> ServerName mysub.domain.edu </VirtualHost> 4) Result of ls -l (when I'm using sudo -i to be root): root@myserver:/home/myusername# ls -l total 4 drwxr-xr-x 2 www-data root 4096 2011-04-18 03:04 htdocs 5) ps auxwww | grep -i apache root@myserver:/home# ps auxwww | grep -i apache root 15121 0.0 0.4 5408 2544 ? Ss 16:55 0:00 /usr/sbin/apache2 -k start www-data 15122 0.0 0.3 5180 1760 ? S 16:55 0:00 /usr/sbin/apache2 -k start www-data 15123 0.0 0.5 227020 2788 ? Sl 16:55 0:00 /usr/sbin/apache2 -k start www-data 15124 0.0 0.5 227020 2864 ? Sl 16:55 0:00 /usr/sbin/apache2 -k start root 29133 0.0 0.1 3320 680 pts/0 R+ 16:58 0:00 grep --color=auto -i apache 6) ls -al /home/myusername/htdocs/ root@myserver:/# ls -al /home/myusername/htdocs/ total 20 drwxr-xr-x 2 www-data root 4096 2011-04-18 03:04 . drw-r--r-- 4 myusername myusername 4096 2011-04-18 02:13 .. -rw-r--r-- 1 root root 69 2011-04-18 02:14 index.html I'm not currently using any .htaccess files in my web root (htdocs) folder in my user folder. I don't know what is wrong, I've been trying to fix his for over 12 hours and I've gotten nowhere. If you have any suggestions, I'm all ears...

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  • A Taxonomy of Numerical Methods v1

    - by JoshReuben
    Numerical Analysis – When, What, (but not how) Once you understand the Math & know C++, Numerical Methods are basically blocks of iterative & conditional math code. I found the real trick was seeing the forest for the trees – knowing which method to use for which situation. Its pretty easy to get lost in the details – so I’ve tried to organize these methods in a way that I can quickly look this up. I’ve included links to detailed explanations and to C++ code examples. I’ve tried to classify Numerical methods in the following broad categories: Solving Systems of Linear Equations Solving Non-Linear Equations Iteratively Interpolation Curve Fitting Optimization Numerical Differentiation & Integration Solving ODEs Boundary Problems Solving EigenValue problems Enjoy – I did ! Solving Systems of Linear Equations Overview Solve sets of algebraic equations with x unknowns The set is commonly in matrix form Gauss-Jordan Elimination http://en.wikipedia.org/wiki/Gauss%E2%80%93Jordan_elimination C++: http://www.codekeep.net/snippets/623f1923-e03c-4636-8c92-c9dc7aa0d3c0.aspx Produces solution of the equations & the coefficient matrix Efficient, stable 2 steps: · Forward Elimination – matrix decomposition: reduce set to triangular form (0s below the diagonal) or row echelon form. If degenerate, then there is no solution · Backward Elimination –write the original matrix as the product of ints inverse matrix & its reduced row-echelon matrix à reduce set to row canonical form & use back-substitution to find the solution to the set Elementary ops for matrix decomposition: · Row multiplication · Row switching · Add multiples of rows to other rows Use pivoting to ensure rows are ordered for achieving triangular form LU Decomposition http://en.wikipedia.org/wiki/LU_decomposition C++: http://ganeshtiwaridotcomdotnp.blogspot.co.il/2009/12/c-c-code-lu-decomposition-for-solving.html Represent the matrix as a product of lower & upper triangular matrices A modified version of GJ Elimination Advantage – can easily apply forward & backward elimination to solve triangular matrices Techniques: · Doolittle Method – sets the L matrix diagonal to unity · Crout Method - sets the U matrix diagonal to unity Note: both the L & U matrices share the same unity diagonal & can be stored compactly in the same matrix Gauss-Seidel Iteration http://en.wikipedia.org/wiki/Gauss%E2%80%93Seidel_method C++: http://www.nr.com/forum/showthread.php?t=722 Transform the linear set of equations into a single equation & then use numerical integration (as integration formulas have Sums, it is implemented iteratively). an optimization of Gauss-Jacobi: 1.5 times faster, requires 0.25 iterations to achieve the same tolerance Solving Non-Linear Equations Iteratively find roots of polynomials – there may be 0, 1 or n solutions for an n order polynomial use iterative techniques Iterative methods · used when there are no known analytical techniques · Requires set functions to be continuous & differentiable · Requires an initial seed value – choice is critical to convergence à conduct multiple runs with different starting points & then select best result · Systematic - iterate until diminishing returns, tolerance or max iteration conditions are met · bracketing techniques will always yield convergent solutions, non-bracketing methods may fail to converge Incremental method if a nonlinear function has opposite signs at 2 ends of a small interval x1 & x2, then there is likely to be a solution in their interval – solutions are detected by evaluating a function over interval steps, for a change in sign, adjusting the step size dynamically. Limitations – can miss closely spaced solutions in large intervals, cannot detect degenerate (coinciding) solutions, limited to functions that cross the x-axis, gives false positives for singularities Fixed point method http://en.wikipedia.org/wiki/Fixed-point_iteration C++: http://books.google.co.il/books?id=weYj75E_t6MC&pg=PA79&lpg=PA79&dq=fixed+point+method++c%2B%2B&source=bl&ots=LQ-5P_taoC&sig=lENUUIYBK53tZtTwNfHLy5PEWDk&hl=en&sa=X&ei=wezDUPW1J5DptQaMsIHQCw&redir_esc=y#v=onepage&q=fixed%20point%20method%20%20c%2B%2B&f=false Algebraically rearrange a solution to isolate a variable then apply incremental method Bisection method http://en.wikipedia.org/wiki/Bisection_method C++: http://numericalcomputing.wordpress.com/category/algorithms/ Bracketed - Select an initial interval, keep bisecting it ad midpoint into sub-intervals and then apply incremental method on smaller & smaller intervals – zoom in Adv: unaffected by function gradient à reliable Disadv: slow convergence False Position Method http://en.wikipedia.org/wiki/False_position_method C++: http://www.dreamincode.net/forums/topic/126100-bisection-and-false-position-methods/ Bracketed - Select an initial interval , & use the relative value of function at interval end points to select next sub-intervals (estimate how far between the end points the solution might be & subdivide based on this) Newton-Raphson method http://en.wikipedia.org/wiki/Newton's_method C++: http://www-users.cselabs.umn.edu/classes/Summer-2012/csci1113/index.php?page=./newt3 Also known as Newton's method Convenient, efficient Not bracketed – only a single initial guess is required to start iteration – requires an analytical expression for the first derivative of the function as input. Evaluates the function & its derivative at each step. Can be extended to the Newton MutiRoot method for solving multiple roots Can be easily applied to an of n-coupled set of non-linear equations – conduct a Taylor Series expansion of a function, dropping terms of order n, rewrite as a Jacobian matrix of PDs & convert to simultaneous linear equations !!! Secant Method http://en.wikipedia.org/wiki/Secant_method C++: http://forum.vcoderz.com/showthread.php?p=205230 Unlike N-R, can estimate first derivative from an initial interval (does not require root to be bracketed) instead of inputting it Since derivative is approximated, may converge slower. Is fast in practice as it does not have to evaluate the derivative at each step. Similar implementation to False Positive method Birge-Vieta Method http://mat.iitm.ac.in/home/sryedida/public_html/caimna/transcendental/polynomial%20methods/bv%20method.html C++: http://books.google.co.il/books?id=cL1boM2uyQwC&pg=SA3-PA51&lpg=SA3-PA51&dq=Birge-Vieta+Method+c%2B%2B&source=bl&ots=QZmnDTK3rC&sig=BPNcHHbpR_DKVoZXrLi4nVXD-gg&hl=en&sa=X&ei=R-_DUK2iNIjzsgbE5ID4Dg&redir_esc=y#v=onepage&q=Birge-Vieta%20Method%20c%2B%2B&f=false combines Horner's method of polynomial evaluation (transforming into lesser degree polynomials that are more computationally efficient to process) with Newton-Raphson to provide a computational speed-up Interpolation Overview Construct new data points for as close as possible fit within range of a discrete set of known points (that were obtained via sampling, experimentation) Use Taylor Series Expansion of a function f(x) around a specific value for x Linear Interpolation http://en.wikipedia.org/wiki/Linear_interpolation C++: http://www.hamaluik.com/?p=289 Straight line between 2 points à concatenate interpolants between each pair of data points Bilinear Interpolation http://en.wikipedia.org/wiki/Bilinear_interpolation C++: http://supercomputingblog.com/graphics/coding-bilinear-interpolation/2/ Extension of the linear function for interpolating functions of 2 variables – perform linear interpolation first in 1 direction, then in another. Used in image processing – e.g. texture mapping filter. Uses 4 vertices to interpolate a value within a unit cell. Lagrange Interpolation http://en.wikipedia.org/wiki/Lagrange_polynomial C++: http://www.codecogs.com/code/maths/approximation/interpolation/lagrange.php For polynomials Requires recomputation for all terms for each distinct x value – can only be applied for small number of nodes Numerically unstable Barycentric Interpolation http://epubs.siam.org/doi/pdf/10.1137/S0036144502417715 C++: http://www.gamedev.net/topic/621445-barycentric-coordinates-c-code-check/ Rearrange the terms in the equation of the Legrange interpolation by defining weight functions that are independent of the interpolated value of x Newton Divided Difference Interpolation http://en.wikipedia.org/wiki/Newton_polynomial C++: http://jee-appy.blogspot.co.il/2011/12/newton-divided-difference-interpolation.html Hermite Divided Differences: Interpolation polynomial approximation for a given set of data points in the NR form - divided differences are used to approximately calculate the various differences. For a given set of 3 data points , fit a quadratic interpolant through the data Bracketed functions allow Newton divided differences to be calculated recursively Difference table Cubic Spline Interpolation http://en.wikipedia.org/wiki/Spline_interpolation C++: https://www.marcusbannerman.co.uk/index.php/home/latestarticles/42-articles/96-cubic-spline-class.html Spline is a piecewise polynomial Provides smoothness – for interpolations with significantly varying data Use weighted coefficients to bend the function to be smooth & its 1st & 2nd derivatives are continuous through the edge points in the interval Curve Fitting A generalization of interpolating whereby given data points may contain noise à the curve does not necessarily pass through all the points Least Squares Fit http://en.wikipedia.org/wiki/Least_squares C++: http://www.ccas.ru/mmes/educat/lab04k/02/least-squares.c Residual – difference between observed value & expected value Model function is often chosen as a linear combination of the specified functions Determines: A) The model instance in which the sum of squared residuals has the least value B) param values for which model best fits data Straight Line Fit Linear correlation between independent variable and dependent variable Linear Regression http://en.wikipedia.org/wiki/Linear_regression C++: http://www.oocities.org/david_swaim/cpp/linregc.htm Special case of statistically exact extrapolation Leverage least squares Given a basis function, the sum of the residuals is determined and the corresponding gradient equation is expressed as a set of normal linear equations in matrix form that can be solved (e.g. using LU Decomposition) Can be weighted - Drop the assumption that all errors have the same significance –-> confidence of accuracy is different for each data point. Fit the function closer to points with higher weights Polynomial Fit - use a polynomial basis function Moving Average http://en.wikipedia.org/wiki/Moving_average C++: http://www.codeproject.com/Articles/17860/A-Simple-Moving-Average-Algorithm Used for smoothing (cancel fluctuations to highlight longer-term trends & cycles), time series data analysis, signal processing filters Replace each data point with average of neighbors. Can be simple (SMA), weighted (WMA), exponential (EMA). Lags behind latest data points – extra weight can be given to more recent data points. Weights can decrease arithmetically or exponentially according to distance from point. Parameters: smoothing factor, period, weight basis Optimization Overview Given function with multiple variables, find Min (or max by minimizing –f(x)) Iterative approach Efficient, but not necessarily reliable Conditions: noisy data, constraints, non-linear models Detection via sign of first derivative - Derivative of saddle points will be 0 Local minima Bisection method Similar method for finding a root for a non-linear equation Start with an interval that contains a minimum Golden Search method http://en.wikipedia.org/wiki/Golden_section_search C++: http://www.codecogs.com/code/maths/optimization/golden.php Bisect intervals according to golden ratio 0.618.. Achieves reduction by evaluating a single function instead of 2 Newton-Raphson Method Brent method http://en.wikipedia.org/wiki/Brent's_method C++: http://people.sc.fsu.edu/~jburkardt/cpp_src/brent/brent.cpp Based on quadratic or parabolic interpolation – if the function is smooth & parabolic near to the minimum, then a parabola fitted through any 3 points should approximate the minima – fails when the 3 points are collinear , in which case the denominator is 0 Simplex Method http://en.wikipedia.org/wiki/Simplex_algorithm C++: http://www.codeguru.com/cpp/article.php/c17505/Simplex-Optimization-Algorithm-and-Implemetation-in-C-Programming.htm Find the global minima of any multi-variable function Direct search – no derivatives required At each step it maintains a non-degenerative simplex – a convex hull of n+1 vertices. Obtains the minimum for a function with n variables by evaluating the function at n-1 points, iteratively replacing the point of worst result with the point of best result, shrinking the multidimensional simplex around the best point. Point replacement involves expanding & contracting the simplex near the worst value point to determine a better replacement point Oscillation can be avoided by choosing the 2nd worst result Restart if it gets stuck Parameters: contraction & expansion factors Simulated Annealing http://en.wikipedia.org/wiki/Simulated_annealing C++: http://code.google.com/p/cppsimulatedannealing/ Analogy to heating & cooling metal to strengthen its structure Stochastic method – apply random permutation search for global minima - Avoid entrapment in local minima via hill climbing Heating schedule - Annealing schedule params: temperature, iterations at each temp, temperature delta Cooling schedule – can be linear, step-wise or exponential Differential Evolution http://en.wikipedia.org/wiki/Differential_evolution C++: http://www.amichel.com/de/doc/html/ More advanced stochastic methods analogous to biological processes: Genetic algorithms, evolution strategies Parallel direct search method against multiple discrete or continuous variables Initial population of variable vectors chosen randomly – if weighted difference vector of 2 vectors yields a lower objective function value then it replaces the comparison vector Many params: #parents, #variables, step size, crossover constant etc Convergence is slow – many more function evaluations than simulated annealing Numerical Differentiation Overview 2 approaches to finite difference methods: · A) approximate function via polynomial interpolation then differentiate · B) Taylor series approximation – additionally provides error estimate Finite Difference methods http://en.wikipedia.org/wiki/Finite_difference_method C++: http://www.wpi.edu/Pubs/ETD/Available/etd-051807-164436/unrestricted/EAMPADU.pdf Find differences between high order derivative values - Approximate differential equations by finite differences at evenly spaced data points Based on forward & backward Taylor series expansion of f(x) about x plus or minus multiples of delta h. Forward / backward difference - the sums of the series contains even derivatives and the difference of the series contains odd derivatives – coupled equations that can be solved. Provide an approximation of the derivative within a O(h^2) accuracy There is also central difference & extended central difference which has a O(h^4) accuracy Richardson Extrapolation http://en.wikipedia.org/wiki/Richardson_extrapolation C++: http://mathscoding.blogspot.co.il/2012/02/introduction-richardson-extrapolation.html A sequence acceleration method applied to finite differences Fast convergence, high accuracy O(h^4) Derivatives via Interpolation Cannot apply Finite Difference method to discrete data points at uneven intervals – so need to approximate the derivative of f(x) using the derivative of the interpolant via 3 point Lagrange Interpolation Note: the higher the order of the derivative, the lower the approximation precision Numerical Integration Estimate finite & infinite integrals of functions More accurate procedure than numerical differentiation Use when it is not possible to obtain an integral of a function analytically or when the function is not given, only the data points are Newton Cotes Methods http://en.wikipedia.org/wiki/Newton%E2%80%93Cotes_formulas C++: http://www.siafoo.net/snippet/324 For equally spaced data points Computationally easy – based on local interpolation of n rectangular strip areas that is piecewise fitted to a polynomial to get the sum total area Evaluate the integrand at n+1 evenly spaced points – approximate definite integral by Sum Weights are derived from Lagrange Basis polynomials Leverage Trapezoidal Rule for default 2nd formulas, Simpson 1/3 Rule for substituting 3 point formulas, Simpson 3/8 Rule for 4 point formulas. For 4 point formulas use Bodes Rule. Higher orders obtain more accurate results Trapezoidal Rule uses simple area, Simpsons Rule replaces the integrand f(x) with a quadratic polynomial p(x) that uses the same values as f(x) for its end points, but adds a midpoint Romberg Integration http://en.wikipedia.org/wiki/Romberg's_method C++: http://code.google.com/p/romberg-integration/downloads/detail?name=romberg.cpp&can=2&q= Combines trapezoidal rule with Richardson Extrapolation Evaluates the integrand at equally spaced points The integrand must have continuous derivatives Each R(n,m) extrapolation uses a higher order integrand polynomial replacement rule (zeroth starts with trapezoidal) à a lower triangular matrix set of equation coefficients where the bottom right term has the most accurate approximation. The process continues until the difference between 2 successive diagonal terms becomes sufficiently small. Gaussian Quadrature http://en.wikipedia.org/wiki/Gaussian_quadrature C++: http://www.alglib.net/integration/gaussianquadratures.php Data points are chosen to yield best possible accuracy – requires fewer evaluations Ability to handle singularities, functions that are difficult to evaluate The integrand can include a weighting function determined by a set of orthogonal polynomials. Points & weights are selected so that the integrand yields the exact integral if f(x) is a polynomial of degree <= 2n+1 Techniques (basically different weighting functions): · Gauss-Legendre Integration w(x)=1 · Gauss-Laguerre Integration w(x)=e^-x · Gauss-Hermite Integration w(x)=e^-x^2 · Gauss-Chebyshev Integration w(x)= 1 / Sqrt(1-x^2) Solving ODEs Use when high order differential equations cannot be solved analytically Evaluated under boundary conditions RK for systems – a high order differential equation can always be transformed into a coupled first order system of equations Euler method http://en.wikipedia.org/wiki/Euler_method C++: http://rosettacode.org/wiki/Euler_method First order Runge–Kutta method. Simple recursive method – given an initial value, calculate derivative deltas. Unstable & not very accurate (O(h) error) – not used in practice A first-order method - the local error (truncation error per step) is proportional to the square of the step size, and the global error (error at a given time) is proportional to the step size In evolving solution between data points xn & xn+1, only evaluates derivatives at beginning of interval xn à asymmetric at boundaries Higher order Runge Kutta http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods C++: http://www.dreamincode.net/code/snippet1441.htm 2nd & 4th order RK - Introduces parameterized midpoints for more symmetric solutions à accuracy at higher computational cost Adaptive RK – RK-Fehlberg – estimate the truncation at each integration step & automatically adjust the step size to keep error within prescribed limits. At each step 2 approximations are compared – if in disagreement to a specific accuracy, the step size is reduced Boundary Value Problems Where solution of differential equations are located at 2 different values of the independent variable x à more difficult, because cannot just start at point of initial value – there may not be enough starting conditions available at the end points to produce a unique solution An n-order equation will require n boundary conditions – need to determine the missing n-1 conditions which cause the given conditions at the other boundary to be satisfied Shooting Method http://en.wikipedia.org/wiki/Shooting_method C++: http://ganeshtiwaridotcomdotnp.blogspot.co.il/2009/12/c-c-code-shooting-method-for-solving.html Iteratively guess the missing values for one end & integrate, then inspect the discrepancy with the boundary values of the other end to adjust the estimate Given the starting boundary values u1 & u2 which contain the root u, solve u given the false position method (solving the differential equation as an initial value problem via 4th order RK), then use u to solve the differential equations. Finite Difference Method For linear & non-linear systems Higher order derivatives require more computational steps – some combinations for boundary conditions may not work though Improve the accuracy by increasing the number of mesh points Solving EigenValue Problems An eigenvalue can substitute a matrix when doing matrix multiplication à convert matrix multiplication into a polynomial EigenValue For a given set of equations in matrix form, determine what are the solution eigenvalue & eigenvectors Similar Matrices - have same eigenvalues. Use orthogonal similarity transforms to reduce a matrix to diagonal form from which eigenvalue(s) & eigenvectors can be computed iteratively Jacobi method http://en.wikipedia.org/wiki/Jacobi_method C++: http://people.sc.fsu.edu/~jburkardt/classes/acs2_2008/openmp/jacobi/jacobi.html Robust but Computationally intense – use for small matrices < 10x10 Power Iteration http://en.wikipedia.org/wiki/Power_iteration For any given real symmetric matrix, generate the largest single eigenvalue & its eigenvectors Simplest method – does not compute matrix decomposition à suitable for large, sparse matrices Inverse Iteration Variation of power iteration method – generates the smallest eigenvalue from the inverse matrix Rayleigh Method http://en.wikipedia.org/wiki/Rayleigh's_method_of_dimensional_analysis Variation of power iteration method Rayleigh Quotient Method Variation of inverse iteration method Matrix Tri-diagonalization Method Use householder algorithm to reduce an NxN symmetric matrix to a tridiagonal real symmetric matrix vua N-2 orthogonal transforms     Whats Next Outside of Numerical Methods there are lots of different types of algorithms that I’ve learned over the decades: Data Mining – (I covered this briefly in a previous post: http://geekswithblogs.net/JoshReuben/archive/2007/12/31/ssas-dm-algorithms.aspx ) Search & Sort Routing Problem Solving Logical Theorem Proving Planning Probabilistic Reasoning Machine Learning Solvers (eg MIP) Bioinformatics (Sequence Alignment, Protein Folding) Quant Finance (I read Wilmott’s books – interesting) Sooner or later, I’ll cover the above topics as well.

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  • Print SSRS Report / PDF automatically from SQL Server agent or Windows Service

    - by Jeremy Ramos
    Originally posted on: http://geekswithblogs.net/JeremyRamos/archive/2013/10/22/print-ssrs-report--pdf-from-sql-server-agent-or.aspxI have turned the Web upside-down to find a solution to this considering the least components and least maintenance as possible to achieve automated printing of an SSRS report. This is for the reason that we do not have a full software development team to maintain an app and we have to minimize the support overhead for the support team.Here is my setup:SQL Server 2008 R2 in Windows Server 2008 R2PDF format reports generated by SSRS Reports subscriptions to a Windows File ShareNetwork printerColoured reports with logo and brandingI have found and tested the following solutions to no avail:ProsConsCalling Adobe Acrobat Reader exe: "C:\Program Files (x86)\Adobe\Reader 11.0\Reader\acroRd32.exe" /n /s /o /h /t "C:\temp\print.pdf" \\printserver\printername"Very simple optionAdobe Acrobat reader requires to launch the GUI to send a job to a printer. Hence, this option cannot be used when printing from a service.Calling Adobe Acrobat Reader exe as a process from a .NET console appA bit harder than above, but still a simple solutionSame as cons abovePowershell script(Start-Process -FilePath "C:\temp\print.pdf" -Verb Print)Very simple optionUses default PDF client in quiet mode to Print, but also requires an active session.    Foxit ReaderVery simple optionRequires GUI same as Adobe Acrobat Reader Using the Reporting Services Web service to run and stream the report to an image object and then passed to the printerQuite complexThis is what we're trying to avoid  After pulling my hair out for two days, testing and evaluating the above solutions, I ended up learning more about printers (more than ever in my entire life) and how printer drivers work with PostScripts. I then bumped on to a PostScript interpreter called GhostScript (http://www.ghostscript.com/) and then the solution starts to get clearer and clearer.I managed to achieve a solution (maybe not be the simplest but efficient enough to achieve the least-maintenance-least-components goal) in 3-simple steps:Install GhostScript (http://www.ghostscript.com/download/) - this is an open-source PostScript and PDF interpreter. Printing directly using GhostScript only produces grayscale prints using the laserjet generic driver unless you save as BMP image and then interpret the colours using the imageInstall GSView (http://pages.cs.wisc.edu/~ghost/gsview/)- this is a GhostScript add-on to make it easier to directly print to a Windows printer. GSPrint automates the above  PDF -> BMP -> Printer Driver.Run the GSPrint command from SQL Server agent or Windows Service:"C:\Program Files\Ghostgum\gsview\gsprint.exe" -color -landscape -all -printer "printername" "C:\temp\print.pdf"Command line options are here: http://pages.cs.wisc.edu/~ghost/gsview/gsprint.htmAnother lesson learned is, since you are calling the script from the Service Account, it will not necessarily have the Printer mapped in its Windows profile (if it even has one). The workaround to this is by adding a local printer as you normally would and then map this printer to the network printer. Note that you may need to install the Printer Driver locally in the server.So, that's it! There are many ways to achieve a solution. The key thing is how you provide the smartest solution!

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  • 10 PowerShell One Liners

    - by BizTalk Visionary
    Here are a few one-liners that use NetCmdlets. Some of these I've blogged about before, some are new. Let me know if you have questions, which ones you find useful, or how you altered these to suit your own needs. Send email to a list of recipient addresses: import-csv users.csv | % { send-email -to $_.email -from [email protected] -subject "Important Email" –message "Hello World!" -server 10.0.1.1 } Show the access control list for a specific Exchange folder: get-imap -server $mymailserver -cred $mycred -folder INBOX.RESUMES –acl Add look and read permissions on an Exchange folder, for a list of accounts pulled from a CSV file: import-csv users.csv | % { set-imap -server -acluser $_.username $mymailserver -cred $mycred -folder INBOX.RESUMES –acl “lr”  } Sync system time with an Internet time server: get-time -server clock.psu.edu –set To remotely sync the time on a set of computers: import-csv computers.csv | % { Invoke-Command -computerName $_.computer -cred $mycred -scriptblock { get-time -server clock.psu.edu –set } } Delete all emails from an Exchange folder that match a certain criteria.  For example, delete all emails from [email protected]: get-imap -server $mailserver –cred $mycred | ? {$_.FromEmail -eq [email protected]} | %{ set-imap -server $mailserver –cred $mycred-message $_.Id -delete } Update Twitter status from PowerShell: get-http –url "http://twitter.com/statuses/update.xml" –cred $mycred -variablename status -variablevalue "Tweeting with NetCmdlets!" A test-path that works over FTP, FTPS (SSL), and SFTP (SSH) connections: get-ftp -server $remoteserver –cred $mycred -path /remote/path/to/checkfor* Don't forget the *.  Also, to use SSL or SSH just add an –ssl or –ssh parameter. List disabled user accounts in Active Directory (or any other LDAP server): get-ldap -server $ad -cred $mycred -dn dc=yourdc -searchscope wholesubtree     -search "(&(objectclass=user)(objectclass=person)(company=*)(userAccountControl:1.2.840.113556.1.4.803:=2))" List Active Directory groups and their members: get-ldap -server testman -cred $mycred -dn dc=NS2 -searchscope wholesubtree -search "(&(objectclass=group)(cn=*admin*))" | select ResultDN, member Display the last initialization time (e.g. last reboot time) of all discoverable SNMP agents on a network: import-csv computers.csv | % { get-snmp -agent $_.computer -oid sysUpTime.0 | %{([datetime]::Now).AddSeconds(-($_.OIDValue/100))} } Not mentioned here:  data conversion (Yenc, QP, UUencoding, MD5, SHA1, base64, etc), DNS, News Groups (NNTP/UseNet), POP mail, RSS feeds, Amazon S3, Syslog, TFTP, TraceRoute, SNMP Traps, UDP, WebDAV, whois, Rexec/Rshell/Telnet, Zip files, sending IMs (Jabber/GoogleTalk/XMPP), sending text messages and pages, ping, and more. Original Source: Lance's Textbox

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  • What is the usage of Splay Trees in the real world?

    - by Meena
    I decided to learn about balanced search trees, so I picked 2-3-4 and splay trees. What are the examples of splay trees usage in the real world? In this Cornell: http://www.cs.cornell.edu/courses/cs3110/2009fa/recitations/rec-splay.html I read that splay trees are 'A good example is a network router'. But from rest of the explanation seams like network routers use hash tables and not splay trees since the lookup time is constant instead of O(log n).

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  • A* navigational mesh path finding

    - by theguywholikeslinux
    So I've been making this top down 2D java game in this framework called Greenfoot [1] and I've been working on the AI for the guys you are gonna fight. I want them to be able to move around the world realistically so I soon realized, amongst a couple of other things, I would need some kind of pathfinding. I have made two A* prototypes. One is grid based and then I made one that works with waypoints so now I need to work out a way to get from a 2d "map" of the obstacles/buildings to a graph of nodes that I can make a path from. The actual pathfinding seems fine, just my open and closed lists could use a more efficient data structure, but I'll get to that if and when I need to. I intend to use a navigational mesh for all the reasons out lined in this post on ai-blog.net [2]. However, the problem I have faced is that what A* thinks is the shortest path from the polygon centres/edges is not necessarily the shortest path if you travel through any part of the node. To get a better idea you can see the question I asked on stackoverflow [3]. I got a good answer concerning a visibility graph. I have since purchased the book (Computational Geometry: Algorithms and Applications [4]) and read further into the topic, however I am still in favour of a navigational mesh (See "Managing Complexity" [5] from Amit’s Notes about Path-Finding [6]). (As a side note, maybe I could possibly use Theta* to convert multiple waypoints into one straight line if the first and last are not obscured. Or each time I move back check to the waypoint before last to see if I can go straight from that to this) So basically what I want is a navigational mesh where once I have put it through a funnel algorithm (e.g. this one from Digesting Duck [7]) I will get the true shortest path, rather than get one that is the shortest path following node to node only, but not the actual shortest given that you can go through some polygons and skip nodes/edges. Oh and I also want to know how you suggest storing the information concerning the polygons. For the waypoint prototype example I made I just had each node as an object and stored a list of all the other nodes you could travel to from that node, I'm guessing that won't work with polygons? and how to I tell if a polygon is open/traversable or if it is a solid object? How do I store which nodes make up the polygon? Finally, for the record: I do want to programme this by myself from scratch even though there are already other solutions available and I don't intend to be (re) using this code in anything other than this game so it does not matter that it will inevitably be poor quality. http://greenfoot.org http://www.ai-blog.net/archives/000152.html http://stackoverflow.com/q/7585515/ http://www.cs.uu.nl/geobook/ http://theory.stanford.edu/~amitp/GameProgramming/MapRepresentations.html http://theory.stanford.edu/~amitp/GameProgramming/ http://digestingduck.blogspot.com/2010/03/simple-stupid-funnel-algorithm.html

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  • New book in the style of Advanced Programming Language Design by R. A. Finkel [closed]

    - by mfellner
    I am currently researching visual programming language design for a university paper and came across Advanced Programming Language Design by Raphael A. Finkel from 1996. Other, older discussions in the same vein on Stackoverflow have mentioned Language Implementation Patterns by Terence Parr and Programming Language Pragmatics* by Michael L. Scott. I was wondering if there is even more (and especially up-to-date) literature on the general topic of programming language design. *) http://www.cs.rochester.edu/~scott/pragmatics/

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  • CPU DB like IMDB for Microprocessors

    - by Jason Fitzpatrick
    If you’re interested in the history of microprocessors, the CPU DB at Stanford is a massive database of microprocessors that covers everything from code names to speed to processor families. Play with their visuals or download the entire database and make your own. CPU DB [Stanford.edu] The Best Free Portable Apps for Your Flash Drive Toolkit How to Own Your Own Website (Even If You Can’t Build One) Pt 3 How to Sync Your Media Across Your Entire House with XBMC

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  • Open Source developers: Need your help to answer an 8-minute academic survey

    - by Yi Wang
    I am a research in University of California, Irvine (UCI). I am conducting a research on collaboration tool usage in Open Source development. Your answers will help us to develop new, powerful tools in future. The link of this survey is: http://edu.surveygizmo.com/s3/1035227/Attitude-and-Usage-of-Collaboration-Tools-in-Open-Source-Software-Development The survey only takes you 5-8 mins. thanks a lot for you help!

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  • What is the usage of Spaly Trees in the real world?

    - by Meena
    I decided to learn about Balance search trees, so I picked 2-3-4 and splay trees. I'm wondering what are the examples of splay trees usage in the real world? In this Cornell: http://www.cs.cornell.edu/courses/cs3110/2009fa/recitations/rec-splay.html I read that splay trees are 'A good example is a network router'. But from rest of the explanation seams like network routers use hash tables and not splay trees since the lookup time is constant instead of O(log n). thanks!

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  • Storing deb packages on local media

    - by Saeid87
    Is there a way to store deb packages (all or a specific version of package) on a local media (dvd, usb etc...) so later I would be able to install those packages on a PC which does not have Internet connection? For example, these are the packages that I want to install on a PC which doesn't have Internet connection: # TinyOS MSP430 GCC Compiler Repository # Version 4.6.3 deb http://tinyprod.net/repos/debian squeeze main deb http://tinyprod.net/repos/debian msp430-46 main # TinyOS version 2.1.2 deb http://tinyos.stanford.edu/tinyos/dists/ubuntu lucid main

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  • What meta tag or microdata should I use for a dictionary web application?

    - by vonPetrushev
    I have a web application that serves as a dictionary, and it ranks good at google when searching for a rare word in my language (the dictionary's target language). I want the result to appear in the define: some-word, as well as in the search results when someone uses the filter tool Dictionary. Should I add some special meta-tag in the head of the html? How about microdata? Does google have a special webmaster tool for registering dictionaries like: wordnetweb.princeton.edu or en.wiktionary.org ?

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  • The Learning Map

    - by user12652314
    Danny Hillis has always been a favorite since he opened the first Java Day back in 1995. Now it's great to see him talking about the challenge we are just about to address with our new "Learning Exchange" Industry Solution which brings all the power of Oracle technology to the address the challenge for lifelong learners. The current thought is to launch it at the Edu tech event at CES along with a special dinner reception with our content friends at Digital Hollywood. Stay tuned.

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  • map a sub page of a domain to google sites

    - by fred
    I control a subpage of a site: economics.university.edu/summerschool I have access to CNAME, etc. However I want to use Google sites to create the site and then map the URL above to my Google site. In other words, someone on the university site that navigated to the summer school page would be redirected to the Google site transparently. However I keep getting this error from Google: "The format of the web address is unsupported." Is this possible?

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  • Getting started with object detection - Image segmentation algorithm

    - by Dev Kanchen
    Just getting started on a hobby object-detection project. My aim is to understand the underlying algorithms and to this end the overall accuracy of the results is (currently) more important than actual run-time. I'm starting with trying to find a good image segmentation algorithm that provide a good jump-off point for the object detection phase. The target images would be "real-world" scenes. I found two techniques which mirrored my thoughts on how to go about this: Graph-based Image Segmentation: http://www.cs.cornell.edu/~dph/papers/seg-ijcv.pdf Contour and Texture Analysis for Image Segmentation: http://www.eng.utah.edu/~bresee/compvision/files/MalikBLS.pdf The first one was really intuitive to understand and seems simple enough to implement, while the second was closer to my initial thoughts on how to go about this (combine color/intensity and texture information to find regions). But it's an order of magnitude more complex (at least for me). My question is - are there any other algorithms I should be looking at that provide the kind of results that these two, specific papers have arrived at. Are there updated versions of these techniques already floating around. Like I mentioned earlier, the goal is relative accuracy of image segmentation (with an eventual aim to achieve a degree of accuracy of object detection) over runtime, with the algorithm being able to segment an image into "naturally" or perceptually important components, as these two algorithms do (each to varying extents). Thanks! P.S.1: I found these two papers after a couple of days of refining my search terms and learning new ones relevant to the exact kind of techniques I was looking for. :) I have just about reached the end of my personal Google creativity, which is why I am finally here! Thanks for the help. P.S.2: I couldn't find good tags for this question. If some relevant ones exist, @mods please add them. P.S.3: I do not know if this is a better fit for cstheory.stackexchange (or even cs.stackexchange). I looked but cstheory seems more appropriate for intricate algorithmic discussions than a broad question like this. Also, I couldn't find any relevant tags there either! But please do move if appropriate.

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  • How to fix footer cutting off content in an above div [closed]

    - by sqyttles
    I am working on this web page: https://ws.missouristate.edu/factbook/execsummary/ and as you can see the page footer is covering the content. I have tried to adjust many CSS properties such as overflow, position, height, float, etc. in firebug and none of my edits have had any positive effect. I am even using a clearing div. Perhaps I am overlooking something pretty easy. How do I prevent the footer from covering up the table content?

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  • Will New Horizons have to bailout?

    - by TATWORTH
    At http://pluto.jhuapl.edu/news_center/news/20121016.php, there is an interesting post about the challenge facing the New Horizons as to whether to allow the spacecraft to remain on the current trajectory which will take it between Pluto and the orbit of Charon, the closest in known moon of Pluto. Given that the current round-trip light time is 6 hrs 53 minutes, a decision to go for a bail-out fly-past must be taken some 10 days in advance of the actual fly-past.

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  • Google I/O Sandbox Case Study: MobileASL

    Google I/O Sandbox Case Study: MobileASL We interviewed MobileASL at the Google I/O Sandbox on May 11, 2011 and they explained to us the benefits of developing their accessibility applications on the Android platform. MobileASL is a video compression project that aims to make sign language communication on mobile phones a reality. For more information on Accessibility Developers, visit: google.com For more information on MobileASL, visit: mobileasl.cs.washington.edu From: GoogleDevelopers Views: 14 0 ratings Time: 01:57 More in Science & Technology

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  • What Are Authority Link Tools?

    In order to establish what an authority link tool is you first have to define what an authority link is. An authority link is a backlink from a website that has standing in the search engines (these are usually .edu or .gov domains).

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  • How to HIDE "client denied by server configuration:" error in log

    - by Keith
    I want to block access to my web server by default as a precaution but I keep getting the following errors showing up in my error log. [Wed Jun 27 23:30:54 2012] [error] [client 86.77.20.107] client denied by server configuration: /home/www/default/Edu.jar [Wed Jun 27 23:32:40 2012] [error] [client 86.77.20.107] client denied by server configuration: /home/www/default/REST.jar [Wed Jun 27 23:35:39 2012] [error] [client 86.77.20.107] client denied by server configuration: /home/www/default/Set.jar [Thu Jun 28 01:01:17 2012] [error] [client 58.218.199.227] client denied by server configuration: /home/www/default/proxyheader.php [Thu Jun 28 02:34:57 2012] [error] [client 58.218.199.227] client denied by server configuration: /home/www/default/proxy.php [Thu Jun 28 05:41:33 2012] [error] [client 58.218.199.227] client denied by server configuration: /home/www/default/proxyheader.php [Thu Jun 28 06:55:10 2012] [error] [client 180.76.6.20] client denied by server configuration: /home/www/default/ [Thu Jun 28 07:31:26 2012] [error] [client 86.77.20.107] client denied by server configuration: /home/www/default/Edu.jar [Thu Jun 28 07:32:25 2012] [error] [client 86.77.20.107] client denied by server configuration: /home/www/default/REST.jar [Thu Jun 28 07:36:10 2012] [error] [client 86.77.20.107] client denied by server configuration: /home/www/default/Set.jar I don't really want these errors to show up but whatever I do, I can't get rid of them. Does anyone know how I can achieve this? Here is a copy of my configuration. <VirtualHost *:80> DocumentRoot /home/www/default <Directory /> AllowOverride None Order Deny,Allow Deny from all </Directory> #ErrorLog /var/log/apache2/error.log #LogLevel warn CustomLog /var/log/apache2/access.log combined </VirtualHost>

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  • /usr/bin/python (Python 2.4) was deleted on CentOS 5. I compiled from source but yum is still broken. How can I get everything back to the way it was?

    - by Maxwell
    I saw a lot of other questions like this but none of them answered the exact part I am having trouble with (actually installing the Python RPM). Someone on my system deleted /usr/bin/python and /usr/bin/python2.4 on my 64 bit CentOS 5.8 installation. I recompiled Python 2.4 from source, but now whenever I try to yum install anything I get the following error: [root@cerulean-OW1 ~]# yum install httpd There was a problem importing one of the Python modules required to run yum. The error leading to this problem was: No module named yum Please install a package which provides this module, or verify that the module is installed correctly. It's possible that the above module doesn't match the current version of Python, which is: 2.4 (#1, Dec 16 2012, 09:16:56) [GCC 4.1.2 20080704 (Red Hat 4.1.2-52)] If you cannot solve this problem yourself, please go to the yum faq at: http://wiki.linux.duke.edu/YumFaq I checked http://wiki.linux.duke.edu/YumFaq and it said the following: If you are getting a message that yum itself is the missing module then you probably installed it incorreclty (or installed the source rpm using make/make install). If possible, find a prebuilt rpm that will work for your system like one from Fedora or CentOS. Or, you can download the srpm and do a rpmbuild --rebuild yum*.src.rpm I tried going to http://rpm.pbone.net/index.php3/stat/4/idpl/17838875/dir/centos_5/com/python-2.4.3-46.el5.x86_64.rpm.html to install Python, which resulted in the following error: [root@cerulean-OW1 ~]# rpm -Uvh python-2.4.3-46.el5.x86_64.rpm error: Failed dependencies: python-libs-x86_64 = 2.4.3-46.el5 is needed by python-2.4.3-46.el5.x86_64 So I tried installing python-libs-x86_64, which resulted in the following: [root@cerulean-OW1 ~]# rpm -Uvh python-libs-2.4.3-46.el5_8.2.x86_64.rpm warning: python-libs-2.4.3-46.el5_8.2.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 192a7d7d Preparing... ########################################### [100%] package python-libs-2.4.3-46.el5_8.2.x86_64 is already installed file /usr/lib64/libpython2.4.so.1.0 from install of python-libs-2.4.3-46.el5_8.2.x86_64 conflicts with file from package python-libs-2.4.3-46.el5_8.2.x86_64

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  • Picking a degree path...

    - by Chris
    I'll be going to University of South Florida soon, and have to choose between two degrees, I want to head into general Server (IT) administration for a small / medium business. Setting up computers, imaging, managing file servers / logon servers /etc. * I had to change the http to hxxp in order to post. I have two degrees I'm currently choosing between: - BSAS hxxp://www.poly.usf.edu/Academics/AppliedAS/BSAS-IT/Program_of_Study.html - BSIT hxxp://www.poly.usf.edu/IT/ I like the idea of a BSAS because it'll get me out sooner, and then I can work on a few certifications to "match" the BSIT... I'm just worried companies will look at that as a "lesser" degree to a BSIT (or even a CS degree.) What are your guys' thoughts on these two degrees? The BSIT has more math, which I still have about 2 more classes to go through (I'll be heading to USF this August.) while the BSIT doesn't require those 2 extra math classes. I keep on hearing from people that when they hire you for your first job, they don't care which degree you have, as long as it's relevant and it's a 4-year degree, is this true?

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  • Server 2003 and XP Client; Why are HTTP connections being silently dropped.

    - by Asa Yeamans
    On my network, my edge-router, a windows 2003 r2 server router with all the latest updates, will drop packets, but only under specific circumstances. I have troubleshot and isolated it down to the most simple configuration i can. There is NO NAT involved. Only fully-public IP addresses. No Firewalls are running either, all ahve been disabled. no packet filters on any interfaces anywhere either. I have a single Windows XP virtual machine and my edge-router(the windows 2003 r2 server, and also a virtual machine) running on a windows 2008 x64 r2 system (running virtual server 2005 as i dont have Intel-VT compatible chip yet). The edge router can access any external http site just fine, no issues. However the windows XP machine is only able to access certain sites. These work: www.google.com www.txstate.edu www.workintexas.com www.thedailywtf.com . These Dont: www.yahoo.com www.utexas.edu en.wikipedia.org slashdot.org www.bing.com. I have removed all possibility of DNS issues by connecting with net-cat from the XP box and sending GET /\r\nHost: \r\n\r\n and that connection replicates the issue as well. The network setup: My statically assigned IP block: x.x.x.168/29 DSL Modem -----PPPoE Connection---- x.x.x.169[EdgeRouter] [EdgeRouter]x.x.x.170 -----Virtual Ethernet----- x.x.x.174 [Test2] Test2's Default gateway is x.x.x.170 and test2 can ping any and every valid, accessible, public IP address with no packet loss what-so-ever. If i connect directly over PPPoE from test2 (the XP box) everything works just fine... Im at my wits end, i have NO IDEA whats causing this.

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  • nginx: Rewrite PHP does not work

    - by Ton Hoekstra
    I've a Suffix Proxy installed and I'm using the following rewrite with wildcard subdomain DNS on: location / { if (!-e $request_filename) { rewrite ^(.*)$ /index.php last; break; } } My suffix proxy has the following URL format: (subdomain and/or domain + domain extension to proxy).proxy.org/(request-uri to proxy) I've this php code in my index.php: if(preg_match('#([\w\.-]+)\.example\.com(.+)#', $_SERVER['SERVER_NAME'].$_SERVER['REQUEST_URI'], $match)) { header('Location: http://example.com/browse.php?u=http://'.$match[1].$match[2]); die; } But when requested a page with a .php extension I'll get a 404 not found error: http://www.php.net.proxy.org/docs.php - HTTP/1.1 404 Not Found http://www.utexas.edu.proxy.org/learn/php/ex3.php - HTTP/1.1 404 Not Found But everything else is working (also index.php is working): http://php.net.proxy.org/index.php - HTTP/1.1 200 OK http://www.php-scripts.com.proxy.org/php_diary/example2.php3 - HTTP/1.1 200 OK http://www.utexas.edu.proxy.org/learn/php/ex3.phps - HTTP/1.1 200 OK http://www.w3schools.com.proxy.org/html/default.asp - HTTP/1.1 200 OK Somebody has an answer? I don't know why it's not working, on apache it's working fine. Thanks in advance. I've removed the location and now it's working perfectly: if (!-e $request_filename) { rewrite ^(.*)$ /index.php last; break; }

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