Copy Directories with Symbolic Links via ssh

25th August 2013

Although probably known in most circles, it is worth repeating that scp by itself does not honor symbolic links. To overcome this limitation just combine tar and ssh, i.e., tar on sending side, untar on receiving side: tar cf - /src/dir | ssh remotehost "cd /dst/dir ; tar xf -" Usually…

Average Size of Web Pages plus Prediction

21st August 2013

Average Size of Web Pages plus Prediction shows an exponential fitting to web-page sizes. From above article: As you can see, the 1/2 MB mark was cracked in 2009 and the 1 MB mark was cracked in 2012. Despite the seemingly random fluctuations, an exponential trend is clearly visible. The power…

SyncSort Sort is Not Stable

15th August 2013

A colleague of mine noticed some strange behaviours in his programs. It was later discovered that this is due to SyncSort not conducting a stable sort. Stable sort means that the sequence of elements in input is not changed if there is no strict need to change them. Unfortunately, the documentation… by the Numbers: The July 2013 Hot List

13th August 2013

Some statistics from WordPress just for month July, 2013. These sheer numbers almost sound unbelievable: 1 million new blogs 7 Exabyte of data 1 billion pages accessed by mobile devices 9 million YouTube videos embedded 500.000 posts per e-mail 200 posts per voice

Design Notes on System for the Analysis of Order- and Stepsize Changes for Cyclic Composite Multistep Methods

11th August 2013

For the numerical solution of the ordinary differential equation, initial value problem $$ y'=f(t,y), \quad y(t_0)=y_0,$$ one can use a cyclic composite multistep method of the form $$ \sum\limits_{i=0}^{m} A_i Y_{k+i} = h \sum\limits_{i=0}^{m} B_i Y'_{k+i}, \qquad…

ssh and rsync for Android

4th August 2013

I got somewhat tired of using FTP with my Android, even with lftp. Keeping multiple folders in sync is simply very cumbersome. If I only had rsync working on Android! I found SSHelper, written by Paul Lutus, see also Arachnoid. SSHelper offers ssh, scp, rsync. You can ssh to your Android phone and…

Google Now Emergency Alert

4th August 2013

When visiting Harvard University I received an Emergency Alert directly on my phone, see below. Google Now Emergency Alert At first I thought that this was a kind of student hack, but others just received the same alerts. After inspection it contained additional information, shown below. Flood…

SUNDIALS (SUite of Nonlinear and DIfferential/ALgebraic equation Solvers)

27th July 2013

Lawrence Livermore National Laboratory provides a suite of software packages for the solution of ordinary differential equations. This suite is called SUNDIALS. SUNDIALS consists of CVODE: solves initial value problems for ordinary differential equation (ODE) systems; successor of GEAR, EPISODE,…

HipHop Virtual Machine can run WordPress

24th July 2013

HipHop Virtual Machine says that HHVM can run WordPress. A more technical description of the HHVM can be found in Speeding up PHP-based development with HipHop VM. One of the main targets was to be as fast as the previous PHP to C++ translater. This goal has been achieved, see graph: Unfortunately…

Blend "Söhne und Weltmacht" and "Why Nations Fail"

19th July 2013

Gunnar Heinsohn (German Wikipedia, English Wikipedia) wrote a book with title Söhne und Weltmacht -- Terror im Aufstieg und Fall der Nationen in German. This book is about: youth bulge and its implication to criminal or war activity genocide property and possession This book can explain why…

Hashing Just Random Numbers

30th June 2013

My recent project had some issues with hashing some 10 million numbers. To analyze the matter I wrote a small test program, see numberhash.c. I wanted to know which influence the following factors play: hashing just numbers (no alphabetic characters) ASCII vs. EBCIDC choice of hash function load…

Very simple SHA1 test program written in C

30th June 2013

Here is a simple test program to call SHA1 hashing routine from OpenSSL. #include <stdio.h> #include <string.h> #include <openssl/sha.h> int main (int argc, char *argv[]) { unsigned long i, n; unsigned char md[1024]; if (argc <= 1) return 0; n…

Hash functions: An empirical comparison -- article by Peter Kankowski

29th June 2013

Peter Kankowski wrote a very interesting article on hashing functions. It compares a number of current hash functions and conducts some performance benchmarks. iSCSI CRC Meiyan Murmur2 XXHfast32 SBox (dead link: Larson XXHstrong32 Sedgewick Novak…

GNU C: Extensions to the C Language Family

29th June 2013

Here is an article GNU C: Extensions to the C Language Family about extensions in GNU C vs. ANSI C. Nested functions, i.e., a function defined within another function Double-word integers, i.e., 64 bit signed and unsigned long long int and unsigned long long int Arrays of variable length, f(int z)…

Memory Limitations with IBM Enterprise COBOL Compiler

22nd June 2013

Recently I learned the hard way that IBM Enterprise COBOL compiler for z/OS (mainframe) cannot generate 8-byte long POINTER variables, but only 4-byte pointers. This means, you cannot use more than 2GB in COBOL on a mainframe. I.e., you cannot make use of AMODE=64 with COBOL on the mainframe. You…

Generators are now in PHP 5.5

21st June 2013

Generators (and therefore coroutines) are now part of PHP (Wikipedia) 5.5, as of 20-Jun-2013. Here is an example: function xrange($start,$end) { for ($i = $start; $i<=$end; ++$i) yield($i); } The Icon programming language (Wikipeda) was one of the first computer languages where…

WordPress Market Share 2011

21st June 2013

I read a short note in Heise, that in 2011 WordPress was one of the most popular CMS. The report compared Alfresco WCM CMSMadeSimple Concrete5 DotNetNuke Drupal e107 eZ Publish Joomla! Liferay MODx Movable Type OpenCms Plone SilverStripe Textpattern Tiki Wiki CMS…

CUDA Performance

19th June 2013

I ran below commands under different load for my Gigabyte GTX 560 graphic card. export LD_LIBRARY_PATH=$CUDA_PATH/lib64 time /usr/local/cuda/samples/sdk/0_Simple/matrixMul/matrixMul time /usr/local/cuda/samples/sdk/0_Simple/matrixMulCUBLAS/matrixMulCUBLAS I was interested in the value…

Kepler’s Hypothesis explained by Brian Koberlein

16th June 2013

I copy Brian Koberlein's explanations in Google+ on the history of Kepler's law. Kepler’s first two rules, that the orbit of a planet is an ellipse, and that a line drawn from the Sun to a planet sweeps out area at a constant rate were proposed in 1609. While these rules allowed for a more…

Running CPU/GPU Intensive Jobs on Titan Supercomputer

16th June 2013

There is a an INCITE program (HPC Call for Proposals), where one can apply for CPU/GPU intensive jobs, the link is INCITE. From the FAQ: The INCITE program is open to US- and non-US-based researchers and research organizations needing large allocations of computer time, supporting resources, and…

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