Getting file/folder list in Windows and Linux

Getting file/folder list in Windows and Linux without using libraries is a tricky business. In Windows Visual Studio, there is also a character set setting (Project properties - Advanced - Character Set) which has to be taken into account.

Vectors for Software Engineers

Vectors are common in simulations but software engineers can forget the basics of vector operations. Here is a quick refresher:

In equation (1), we have a velocity vector of point m with respect to point c, expressed as a sum of two vectors.

In equation (2), we have the same equation but in scalar form. The "(n)" represents the reference frame in which the components of the vectors are expressed. In order to perform addition, all vector components must be expressed in the same reference frame.

If you want more detail, check out my advanced dynamics lecture notes (PDF).

Generate C/C++ Code From Matlab Function

Use MATLAB Coder to generate C/C++ code from an m file (must be a function). At the end of the process, click on "View Report" and on the Report Viewer window, click on Package Code to package all the dependencies (e.g. tmwtypes.h) into a single zip file.

Check if the MATLAB instance you created has exited

When you run MATLAB from a Windows bat file and want to know if it has finished its job and exited (without considering other already open MATLAB instance), you can use the following:

start matlab.exe -nosplash -nodesktop -noFigureWindows
set pid=not found
for /f "tokens=2" %%a in ('tasklist^|find /i "matlab") do (set pid=%%a)
echo matlab pid = %pid%

:waitForMatlabToExit
timeout /t /5 /nobreak
tasklist /fi "pid eq %pid%" | find ":">nul
if errorlevel 1 goto waitForMatlabToExit
echo Matlab exited
exit /b

Windows batch file: goto vs call

In a Windows batch file, goto label2 command goes to the label2 and continues from the end of label2. call :label2 goes to label2 and after seeing a exit /b (or end of script, eof), returns back right after the call command. In other words, call behaves like a function call in Java, C++ etc. but you have to use exit /b instead of return.

Calling a Matlab function from Windows command line (cmd)

Calling a Matlab function from a Windows cmd batch file is easy if the function has no string arguments. However if the function takes a string argument, you have to use two single quotes around the argument. Example:

start matlab -nosplash -nodesktop -noFigureWindows -r eval("'myFunction(''fileName.txt'')'")

Bundling JavaScript dependencies into a single JS file

To bundle/embed/include all JS dependencies into a single JS file, you can use webpack.

Module Bundlers Explained... Webpack, Rollup, Parcel, and Snowpack

Remote connection and file transfer

The easiest way to connect from Windows to a remote Linux computer is to fire up cmd.exe and type ssh user@ip where user is the Linux user name and ip is the IP address of the Linux computer. 

For file transfer, you can use sftp user@ip or scp fileName user@remoteIP/remoteFileName.

ssh, sftp and scp come with Windows 10, you don't have to install anything. Just make sure that SSH is enabled on Linux.

Simple way/pattern to separate GUI from model

Prepare your model as a separate executable that reads input from file and writes output to a file. Then you can code your GUI in whatever language you like (e.g. Excel macros) that takes input from user, writes them to file, runs the model executable and reads outputs from file when executable finishes.

This completely decouples GUI from implementation. Compared to a DLL, it has a simpler interface, it will not crash your JVM if there is an error in model, and let's you run models in parallel much easier and also facilitates easy batch run of model executable via scripts.

Debugging Effort

The hardest part of debugging is finding the root cause of the problem, therefore it is wise to optimize code for debugging, see clean code:

memcpy() vs memmove()

When you need to implement removal of an element from an arraylist, don't use memcpy, use memmove. Your program might run fine on Windows but cause trouble in Linux, whose root cause would be hard to find.

memcpy() vs memmove(): in case of memcpy(), there is no extra buffer taken for source memory. The copying is done directly on the memory so that when there is memory overlap, we get unexpected results. 

Simulink versions

Matlab release - Simulink version (helpful when you know the Simulink version and wonder which Matlab release it corresponds to):

Safety-Critical System Development

Safety-critical system development requires safety certification. Examples for railways are EN 50128 (software) and EN 50129 (hardware). For aerospace there are DO-178 (software) and DO-254 (hardware). Since it it not practically possible to have 100% test coverage for complex systems, these documents require that development processes adhere to practices that minimize risk of catastrophic failure.

Companies with no experience in these standards grossly underestimate time and budget requirements of making the necessary changes for compliance. It takes at least two years to get a company from zero to certified. If the company has the vision to enter the aerospace market, compliance preparations have to be started before any system development contract, because to both change company culture and develop the system at the same time is a sure way to fail.

One way to avoid these standards is to come up with a simple design, provided that the requirements are simple enough. For example, an aircraft climate controller consisting of temperature and airflow sensors and fan and valve actuators could be realized with a simple PID controller using only operational amplifiers. Since it has no software and the relatively simple hardware can be tested with 100% coverage, there is no need to demonstrate that company development processes are sound.

Binary string permutations

Previously, I had solved printing all permutations of a string. As part of a programming contest, I solved binary string permutations using C++. What is interesting in this solution is that is uses a simple for loop and obtains each binary permutation by converting a decimal number to a binary number:

Hiding internal details of a C++ library

When you need to provide your simulation as an external library (dll, lib) to someone, you should simplify the API as much as possible so that you are able to provide the minimal amount of header files, without exposing details the user doesn't care about. You can achieve this by hiding all the internal dependencies in the implementation (cpp) file. If the user has to be able to create multiple (concurrent) simulations, you can use a static map to hold each simulation object. Here is an example (C++11):

C++: Using 1 byte enum

By default, enum size in C++ is usually 4 bytes, both in Windows and Linux. If you need to use 1 byte enum, you have to declare it as follows:

enum e : unsigned char { a, b };

This requires at least C++ 11. printf("size = %ld\n", sizeof(e)) will output 1.

If you are using gcc (e.g. Eclipse), you can also use the compiler flag -fshort-enum (Eclipse properties - C/C++ Build - Settings - Tool Settings - GCC C++ Compiler - Miscellaneous) to convert all enums in code to 1 byte, but you won't have that option in Visual Studio. So it is better to use the unsigned char option.

Use memset only with zero

Consider the following C++ definitions:

typedef struct {

int i;

double d[3];

} A_STRUCT

A_STRUCT s;

When I use memset(&s, 0, sizeof(s)), i and d values are set to zero as expected. When I use memset(&s, -1, sizeof(s)), I would expect all values to be -1 but on inspection you will see that they have strange values, in my case i was -1 but d values were -nan. When I use memset(&s, 1, sizeof(s)), I get 16843009 for i and 7.74...e-304 for d values.

Reason: The memset() function writes bytes, not words. So writing 1 to sizeof(int)*100 bytes writes 00000001 to every set of 8-bits.Thus, each integer in binary looks like the following:

0000 0001 0000 0001 0000 0001 0000 0001 (1 int = 4 bytes)

which in decimal is, exactly, 16843009..

memset doesn't only work with 0. It also works with all numbers with identically repeating byte pattern. Like for example ~0.

#define considered harmful

 In C++, #define has global scope. If you have a #define FAIL (-1) in a header file that you include, you cannot declare a variable named FAIL anywhere else, not even inside a namespace. If you do, you will get the cryptic error message "expected an identifier":

So, don't use define for named constants in C++, use const int etc. If you are using C instead of C++, read this.