One puzzling error that happens, albeit rarely, is having too many file handles open at the same time. You can check the limit allowed per process on your system by doing The key value is “open files” which, in my case, is limited to 256. In my application I was running into this. (As a… Read More Too many open files
Install Perl from the Synology package manager Use curl to download the *nix distribution to a folder (instruction here) make is not present on the Synology, but we don’t need it. Copy exiftool and lib directory to a directory of your choosing, or leave it where it is, if you won’t erase it Use vi… Read More Install exiftool on Synology
In my spacecraft simulator all the ships start out orbiting something. So, at the start of the simulation I need to compute a position and velocity for each ship that places them in stable orbit round a chosen body. It is straightforward to compute the initial position and velocity for a circular orbit: the centrifugal… Read More Elliptical orbit math
C++17’s std::filesystem gives me the warm fuzzy feeling Python3’s pathlib does. Easy, intuitive and cross-platform, yet another excuse to use C++17. Don’t look back. Just use it. Specially useful functions in std::filesystem are: The / operator : The committee fought their instincts to be “enterprise” , decided to be more Pythonic, and got this very… Read More Just use std::filesystem
The vast majority of our software applications are driven by graphical user interfaces. There is a certain charm, however, to doing, or driving, things using a text file. I’m not talking about things like computer code, or software configurations being written in text files. I’m talking about using text files to drive an application that… Read More Text file driven applications
Many scientific computing applications consist of processing data and then writing out to disk. Often the application will be I/O bound, which means that the computation time is shorter that the time it takes to read or write data to disk. Even though modern OSes do their best to write efficiently to the hardware, there… Read More Buffering writes
One of the unexpected side-effects of our attempt to fire-break #COVID19 with #PhysicalDistancing , is the absence of laughter in the late night shows I like to watch. This lack of laughter taught me some interesting things about my reactions to these shows, and gave me extra admiration for how @StephenAtHome and @iamjohnoliver
are now doing the shows with no live feedback. … Read More Laughter, groupthink and physical distancing
Compilers have options that allow you to retain and inspect a disassembly of the generated machine code. On macOS, passing the gcc compiler the options -fverbose-asm -save-temps will tell the compiler to write out a file with the assembly code interspersed with the original source code. As an example, the file compiled with c++ -c… Read More Stream-of-consciousness note on disassembly
Using matrix multiplication as an example, we explore how computation speed is dramatically affected by how data is laid out in memory.… Read More CPU caches and data locality: a small demonstration
C++ is an object oriented language. So is Python. Python in my opinion handles most object oriented concepts much more elegantly than C++. Here is a small example. (Well, both are sold as multi-paradigm languages, which means they do a bit of everything. C++ has tail call optimization and Python has lambdas and functions are… Read More A certain awkwardness with C++ inheritance
If you define a function in a header file (i.e. have it’s implementation in the header) and statically link your program, you need to declare it inline if the header is used in multiple files. This is different from issues you get when a header file is included multiple times in a compilation unit. Consider… Read More static linking, duplicate symbol error and inlineing
Mixing up units is a very common problem everywhere. A formula takes meters, you put in feet and your Mars probe crashes. It happens. In C++ there are “zero cost” libraries to handle full-fledged dimensional checking, conversions and safeguards. How do they work? Are they really zero cost? Let’s explore using a simple limited example,… Read More Simple units checking for cheap in C++
Digital Apollo is a excellent sociological and technological study of the uneasy alliance between the astronauts who commanded the Apollo missions, and the computers which actually controlled the spacecraft systems. It traces how pilots, who first resisted the incursion of computers into their domain, gradually and grudgingly accepted the important role the computers played in… Read More Digital Apollo – Mindell (2008)
Currently, robotic spacecraft give us enormously more scientific and engineering value than manned missions. We should only invest in manned space flight once there is a clear rationale for a continuous manned presence in space. When Boeing figured out that bad time data caused Starliner to waste precious propellant during orbit insertion, making it infeasible… Read More We should not be wasting money on manned space missions.
In my earlier post I left off with the suggestion that I would get the Olympus 45mm f1.8 lens. I got a bit side tracked by an adventure with a Nikon F mount adapter, but I’m back now and I have a completely different plan. I abandoned my idea of getting a longer focal length… Read More Picking a prime for the 4/3 (Pt II)
While trying to figure out if I should splurge on a new lens for my E-M10 I re-discovered the joys of my old Nikon lenses thanks to a $16 adapter and the magic of my E-M10. SLR lenses on mirrorless micro 4/3 cameras are an especially good marriage because of the small flange distance of… Read More Old school on the E-M10
I don’t know how to play an instrument. I can’t read musical notation. I can’t sing or whistle. But when we got a piano in our home, I dared to dream that I could one day learn to play on it. So, how to start? A friend said “Hire a piano teacher.” That’s probably what anyone… Read More Learning piano
Apparently I have enough money saved up from several years of Christmas and birthday vouchers from relatives to buy myself something fun. Not practical things, like socks and trousers, but something fun. So I decided it was going to be a lens for the Olympus E-M10. I mostly take pictures of family. I mostly take… Read More Picking a prime for the 4/3
Do you want to hear about that one time all the apparatus of modern software engineering – unit tests and continuous integration – actually helped the programmer to break code, rather than fix it? I was working on some code a bunch of other people wrote. It wasn’t a particularly large code base, but it… Read More Overfitting code to the unit tests
DragonBox algebra is a cool iPad game that teaches the mechanics of algebra in a very clever manner. The player is presented with a field divided into two halves. There is a magic box card (marked with a star) on one side (though on later levels you can suddenly see several of these boxes. These… Read More DragonBox Algebra
