Getting FreeFem++ to display impressive visuals under Linux.

One of my Computing habits is, to acquire many frameworks, for performing Scientific or Analytical Computing, even though, in all honesty, I have little practical use for them, most of the time. They are usually of some Academic curiosity to me.

Some of the examples familiar to me are, ‘wxMaxima‘ (which can also be installed under Linux, directly from the package manager), ‘Euler Math Toolbox‘ (which, under Linux, is best run using Wine), and ‘SageMath‘ (which IMHO, is best installed under Linux, as a lengthy collection of packages, from the standard repositories, using the package manager, that include certain ‘Jupyter’ packages). In addition to that, I’d say that ‘Python‘ can also be a bit of a numerical toolbox, beyond what most programming languages can be, such as C++, yet, a programming language primarily, which under Linux, is best installed as a lengthy collection of packages through the package manager. And a single important reason is the fact that a Python script can perform arbitrary-precision integer arithmetic natively, and, with a small package named ‘python3-gmpy2′, can also perform arbitrary-precision floating-point arithmetic easily. If a Linux user wanted to do the same, using C, he or she would need to learn the library ‘GMP’ first, and that’s not an easy library to use. Also, there exists IPython, although I don’t know how to use that well. AFAICT, this consists mainly of an alternative shell, for interacting with Python, which makes it available through the Web-interface called “Jupyter”. Under Debian Linux, it is best installed as the packages ‘ipython3′, ‘python3-ipython-genutils’, ‘python3-ipykernel’, ‘python3-nbconvert’, and ‘python3-notebook’, although simply installing those packages, does not provide a truly complete installation… Just as one would want a ‘regular’ Python installation to have many additional packages, one would want ‘IPython’ to benefit from many additional packages as well.

But then, that previous paragraph also touches on an important issue. Each Scientific Computing platform I learn, represents yet-another scripting language I’d need to learn, and if I had to learn 50 scripting languages, ultimately, my brain capacity would become diluted, so that I’d master none of them. So, too much of a good thing can actually become a bad thing.

As a counter-balance to that, it can attract me to a given Scientific Computing platform, if it can be made to output good graphics. And, another Math platform which can, is called “FreeFem“. What is it? It’s a platform for solving Partial Differential Equations. Those equations need to be distinguished from simple derivatives, in that they are generally equations, in which a derivative of a variable is being stated on one side (the “left, bilinear side”), but in which a non-derivative function of the same variable is being stated on the other (the “right side”). What this does, is to make the equation a kind of recursive problem, the complexity of which really exceeds that of simple integrals. (:2)  Partial Differential Equations, or ‘PDE’s, are to multi-variable Calculus, as Ordinary Differential Equations, or ‘ODE’s, are to single-variable Calculus. Their being “partial” derives from their derivatives being “partial derivatives”.

In truth, Calculus at any level should first be studied at a University, before computers should be used as a simplified way of solving its equations.

FreeFem is a computing package, that solves PDEs using the “Finite Element Method”. This is a fancy way of saying, that the software foregoes finding an exact analytical solution-set, instead providing an approximation, in return for which, it will guarantee some sort of solution, in situations, where an exact, analytical solution-set could not even be found. There are several good applications. (:1)

But I just found myself following a false idea tonight. In search of getting FreeFem to output its results graphically, instead of just running in text mode, I next wasted a lot of my time, custom-compiling FreeFem, with linkage to my many libraries. In truth, such custom-compilation is only useful under Linux, if the results are also going to be installed to the root file-system, where the libraries of the custom-compile are also going to be linked to at run-time. Otherwise, a lot of similar custom-compiled software simply won’t run.

What needs to be understood about FreeFem++ – the executable and not the libraries – is, that it’s a compiler. It’s not an application with a GUI, from which features could be explored and evoked. And this means that a script, which FreeFem can execute, is written much like a C++ program, except that it has no ‘main()‘ function, and isn’t entirely procedural in its semantics.

And, all that a FreeFem++ script needs, to produce a good 2D plot, is the use of the ‘plot()‘ function! The example below shows what I mean:

 

Screenshot_20210708_232521

 

I was able to use an IDE, which I’d normally use to write my C++ programs, and which is named “Geany”, to produce this – admittedly, plagiarized – visual. The only thing I needed to change in my GUI was, the command that should be used, to execute the program, without compiling it first. I simply changed that command to ‘FreeFem++ "./%f"‘.

Of course, if the reader wants in-depth documentation on how to use this – additional – scripting language, then This would be a good link to find that at, provided by the developers of FreeFem themselves. Such in-depth information will be needed, before FreeFem will solve any PDEs which may come up within the course of the reader’s life.

But, what is not really needed would be, to compile FreeFem with support for many back-ends, or to display itself as a GUI-based application. In fact, the standard Debian version was compiled by its package maintainers, to have as few dependencies as possible (‘X11′), and thus, only to offer a minimal back-end.

(Updated 7/14/2021, 21h45… )

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Getting the integrated equalizer to work, from Debian Jessie, KDE 4.

I happen to have an older laptop, which I name ‘Klystron’, that is running Debian 8 / Jessie, with KDE 4 as its desktop manager. Don’t ask me why, but I tend to leave older builds of Linux running on some of my computers, just because they seem to be running without any deficiencies.

That laptop has lousy speakers. I decided a few days ago, that it would benefit, if I could get the 14-band graphical equalizer to work, that is generally available on Linux computers which, like that laptop, use the ‘PulseAudio’ sound server. However, on this old version of Linux, achieving that was a bit harder than it’s supposed to be. Yet, because I succeeded, I felt that I should share with the community, what the steps were, needed to succeed.

First of all, this is what the equalizer looks like, which I can now open on that laptop:

Equalizer_1

And it works!

 

In order to get this sort of equalizer working with PulseAudio, eventually, the following two modules need to be loaded:

module-equalizer-sink

module-dbus-protocol

And, if I gave the command ‘load-module…’ naively from the command-line, as user, because under my builds of Linux, PulseAudio runs in user mode, both these modules seem to load fine, without my having to install any additional packages.

On more recent builds of Linux, one needs to install the package ‘pulseaudio-equalizer’ to obtain this feature, or some similarly-named package. But, because these two modules just loaded fine under Debian / Jessie, I guess the functionality once came integrated with PulseAudio.

But I soon started to run in to trouble with these modules, and discovered why, then, the equalizer function was not set up to run out-of-the-box…

(Updated 6/26/2020, 10h30… )

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Exploring the newer GUI front-end, for use with SageMath.

One of the subjects which I had written about only yesterday, is that the Computer Algebra / Numerical Tool System called ‘SageMath‘ was available in the repositories, for Debian / Stretch – which is in itself news – and that additionally, the default way to use it under Debian is through a Web-interface called ‘SageNB’. Well what I’ve now learned is that the SageMath developers no longer support SageNB, and are continuing their work with the graphical front-end called ‘Jupyter‘.

But, installing Jupyter under Debian is a bit of a chore, because unlike how it is with custom-compiles, Debian package maintainers tend to break major software down into little bits and pieces. At one point, I had Jupyter running, but with no awareness of the existence of SageMath. What finally did the trick for me today, was to install the following packages:

  • python-notebook
  • jupyter-nbextension-jupyter-js-widgets
  • sage-math-jupyter

Needless to say, that last package out of the three is the most important, and may even pull in enough of the other packages, to be selected by itself. It’s just that I did not know immediately, to install that last package.

So this is what SageMath 7.4 looks like, through Jupyter:

screenshot_20180916_165217

(Corrected 09/18/2018, 3h50 … )

(Updated 09/18/2018, 5h40 … )

(As of 09/16/2018, 20h10 : )

Frankly, I was a bit disappointed at first. My main disappointment seemed to be with the fact, that this GUI did not offer to typeset the Math. It does allow us to ‘download’ our Notebooks as PDF-Files, but when we do, we simply get the same, highlighted text, and graphics, only as a PDF – in code – or with whatever appearance the browser-view is already showing us. Also, the support for 3D plots is lackluster, as the plot above is non-interactive. At least with SageNB, I was able to select the ‘canvas3d’ viewer, which allowed the plot to be rotated. Also, if we use SageMath from the command-line, it defaults to using ‘JMol’ as its viewer, which is full-featured.

But as it turns out, I have discovered ‘the trick’, to getting Jupyter to typeset the users’ Math…

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File-Sharing under Linux, using Usershares – the Modernistic Way.

One concept which readers may already know, is that under Linux, we can set up a Samba-server, which makes the sharing-out of our home directories possible, and that if we fiddle with the ‘smb.conf’ configuration file thoroughly enough, it becomes possible to browse the available shares on a LAN, in a way semi-compatible with Windows computers that also reside on the same LAN.

Traditionally, this has always been a bit of a PITA, especially since the ‘/etc/samba/smb.conf’ configuration files have been finicky, and since each share practically needs to be configured individually, by a person with the ‘root’ password.

Well an alternative exists under Linux as well, which is the concept of ‘Usershares’. With this concept, each user who belongs to a specific group has the privilege, of designating a folder within his desktop manager, to share out, pointing-and-clicking. This is closer in ease-of-use, to how the process works under Windows. But, it needs to be set up correctly once, by the sysadmin, before it will work as often as simple users wish it to work.

I think that an existing Web-article on the subject, already explains well, what the settings in the ‘smb.conf’ file need to be, as well as what directories need to exist, in order for usershares to work. Except that the article I just linked to, refers to Fedora and SELinux systems and their norms. I happen to be based on Debian and KDE 4 or Plasma 5. And so I have a few observations to add:

Firstly, the following packages should be installed, under Debian also:

 


#apt-get install kdenetwork samba

 

Secondly, ‘/etc/samba/smb.conf’ needs to be edited like so:

 

screenshot_20180324_205625

 

Under Debian, the directory ‘/var/lib/samba/usershares’ already exists, If the relevant packages are installed. And its permission-bits have already been set as they should be set. Only, the feature is not configured in ‘smb.conf’ by default. And, the additional package named ‘kdenetwork-filesharing’ needs to be installed, in order for the tab to appear in Dolphin’s File-Properties box, that enables sharing from the GUI. Aside from that, enabled users need to be added to the ‘sambashare’ group, after which this membership only goes into effect, once the user in question has started a new session…

(Info Corrected 03/25/2018, 17h10,

Updated again 03/28/2018 … )

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