I was wondering which high-level langunage allows the easiest manner in which to call Fortran subroutines? I currently use MATLAB and calling MEX files seems to be relatively complicated compared to other languages.
I'm particularly interested in how the following compares in terms of getting "up and running" quickly:
*Python via f2py
*R via ?
*MATLAB via MEX files
Another way of asking this would be "If you were to start over and learn a new language, which one would you choose if your objective was calling Fortran subroutines?"
I'm trying to getbthe "best of both worlds" i.e. having good data handling and graphics combined with the ability to call fast Fortran subroutines.
Thank you all in advance for any help you can provide. Alas, if someone knows of a good MEX tutorial for Fortran, that would be appreciated as well.
I was wondering which high-level langunage allows the easiest manner in which to call Fortran subroutines?
The obvious answer is Fortran itself. So-called Modern Fortran (2003 & 2008) has a lot of high-level features. And obviously it's easy to call legacy FORTRAN code (my guess is that you have old FORTRAN code base) from the modern one.
Python via f2py is very nice. I had a little bit of trouble getting it going on Windows with IVF, but it didn't take long to figure out, and the mailing list gives prompt responses. On Linux, it worked without any issues.
I haven't used R, but as I understand it, it's only useful if you do a lot of statistics with large amounts of data. As for MATLAB, it's a horrible language, if you're just calling FORTRAN, you're better off with Python.
What I usually do in your case is create Fortran programs that I can pass command line arguments to as input. This is readily available by Fortran 2003 standard using intrinsic get_command_argument subroutine. You can then parse Fortran program output from whatever language you are using as a wrapper (assuming language has access to system shell). In the past, I did this with shell scripts, MATLAB (avoid), Python.
Related
I know that many large-scale applications such as video games are created using multiple langages. For example, it's likely the game/physics engines are written in C++ while gameplay tasks, GUI are written in something like Python or Lua.
I understand why this division of roles is done; use lower-level languages for tasks that require extreme optimization, tweaking, efficiency and speed, while using higher-level languages to speed up production time, reduce nasty bugs ect.
Recently, I've decided to undertake a larger personal project and would like to divy-up parts of the project similar to above. At this point in time, I'm really confused about how this interoperability between languages (especially compiled vs interpreted) works.
I'm quite familiar with the details of going from ANSCII code test to loading an executable, when written in something like C/C++. I'm very curious at how something like a video game, built from many different languages, works. This is a large/broad question, but specifically I'm interested in:
How does the code-level logic work? I.e. how can I call Python code from a C++ program? Especially since they don't support the same built-in types?
What does the program image look like? From what I can tell, a video game is running in a single process, so what does the runtime image look like when running a C/C++ program that calls a Python function?
If calling code from an interpreted language from a compiled program, what are the sequence of events that occur? I.e If I'm inside my compiled executable, and for some reason have a call to an interpreted language inside a loop, do I have to wait for the interpreter every iteration?
I'm actually finding a hard time finding information on what happening at the machine-level, so any help would be appreciated. Although I'm curious in general about interoperation of software, I'm specifically interested in C++ and Python interaction.
Thank you very much for any insight, even if it's just pointing me to where I can find more information.
In the specific case of python, you have basically three options (and this generally applies across the board):
Host python in C++: From the perspective of the C++ programme, the python interpreter is a C library. On the python side, you may or may not need to use something like ctypes to expose the C(++) api.
Python uses C++ code as DLLs/SOs - C++ code likely knows nothing of python, python definitely has to use a foreign function interface.
Interprocess communication - basically, two separate processes run, and they talk over a socket. These days you'd likely use some kind of web services architecture to accomplish this.
Depending on what you want to do:
Have a look at SWIG: http://www.swig.org/ It's a tool that aims to connect C/C++ code with Python, Tcl, Perl, Ruby, etc. The common use case is a Python interface (graphical or not) that will call the C/C++ code. SWIG will parse the C/C++ code in order to generate the interfaces.
Libpython: it's a lib that allows you to embed Python code. You have some examples here: http://docs.python.org/3.0/extending/embedding.html
I would like to embed a scripting language(js, python, perl, even php, anything that's easy to use) in an OpenGL C++ application. I'd like to do this in order to be able to do things like:
print values of various C++ class members at runtime
cause interrupts that would wake up gdb at runtime
after I find a bug I'd like to write a small script oneliner to replicate it
I'm pretty sure this won't be easy. I want to ask whether this is a good/bad idea, and if it's worth the effort.
Example usecase
Let's suppose I rotate a line until it collides something and my collision detection has some SIGSEGV which occurs upon collision. I print out all the angles, find out which one was the one before the SIGSEGV and I write a small python thingie which displays some values so I can figure out what went wrong etc.
I guess basically What I'm trying to do is to avoid gdb and uhm.. I'd like if the program blows to have a way to check things in Python instead.
It's not that I don't like gdb, it's that I don't like the limited commands it has..
UPDATE: GDB can now be extended with Python out of the box. That solves a lot of the limitations of canned sequences of commands.
I don't think that for the purpose of debugging embedding a scripting language is a good idea. It's definitely possible, but for everything that you'd want to be able to access from the scripting language, you would have to provide some interface, since there's -- to the best of my knowledge at least -- no way to directly call C++ or read C++ data structures from a scripting language. I'd suggest you learn gdb or look for gdb frontends if you don't want to use gdb directly. I've used ddd and found it quite useful. The gdb frontend of Eclipse CDT is usable, too. Using a debugger gives you more flexibility, since the debugger knows about C++ and its data structures and thus allows you to inspect anything at runtime, without having to manually write much support code for that.
First of all: You can print all those out using GDB quite easily. Once in GDB you might want to try what "help data" shows.
Which IDE do you use? You might want to try the cross-platform IDE Code::Blocks, which interfaces GDB quite neatly.
If you want to interface with another language, you might want to have a look on "Lua". It is very easy to learn.
See http://en.wikipedia.org/wiki/Lua_%28programming_language%29
Lua is intended to be embedded into other applications, and accordingly it provides a robust, easy-to-use C API. The API is divided into two parts: the Lua core and the Lua auxiliary library.
This works well with C++, too, of course.
i can´t help with the questions if it´s a good or bad idea.
but you could take a look at Chaiscript that´s really easy to use with c++
Python is a very good choice as application scripting language. Its not a strong argument but I know that lua is widely used in game programming (I d'ont know why), it may be useful since you are using OpenGL.
Use lua - it's simple stack based interpreter. With very clean API.
E.g.: Simple code that add dt_format|dt_convert functions to lua
I've got some code I need to run, written in FORTRAN IV. What are my options for running this code? Is there an application out there that can compile and run FORTRAN IV code on a PC? Or if possible I am looking for a utility to convert Fortran IV code to FORTRAN 77 or later. I have little experience in Fortran and in programing in general.
Thanks for you help
Intel's Fortran compiler supports Fortran IV. If you don't want to go that way, there are some conversion utilities mentioned in this question --- but none of them sound very promising.
Very few features have been deleted from Fortran. A few more features have been marked as obsolescent in the more recent language standards. But the compilers tend to support most or all of these features because some customers don't want to recode working legacy programs just because they use "bad" features. Sometimes one has to use compiler options to use some of these features. So I'd just pick a compiler and try it on the existing code. There are many to choose from. Maybe get a trial version to see whether it works before paying your money or use a free one.
Another possible problem is that your code base might have non-standard features. In pre Fortran-90 days there was less concern with language standards and some vendors added extra features for user convenience and to differentiate their product. If present, such features might cause greater problems and require recoding.
Probably the most important feature of Fortran IV is that do loops check the variable at the end. Thus do loops always execute at least once. This was a big issue when it was changed to the current method.
n = 5
do 99 i = n, 4
write(*,*) i
99 continue
Will print out "5" in Fortran IV, and nothing in Fortran 77. Codes that use this feature can be hard to port.
I'll just add that if the code does use non-standard features that your compiler doesn't handle, the maintainers at fortranwiki.org maintain a nice list of explanations of, and workarounds for, many such contstructs on their Modernizing Old Fortran page.
The obvious answer is to run it as is on MVS 3.8J under the Hercules emulator. MVS 3.8J and IBM FORTRAN G and FORTRAN H are public domain.
You will be able to compile and run the code as if you had a real mainframe! The IBM FORTRAN compilers support (defined, actually) the full FORTRAN IV language along with IBM extensions.
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I'm doing a Windows Application the uses lots of charts. Its practically a dataviewer. I started doing Matlab, because its easier, but I realized it's too slow. I wanted to change to another language. Somebody recommended me Visual C++ or Java. But Im not sure. What language should I use??
In my opinion the speed gain from going to another "faster" language is not as much as refining your algorithm.
The "problem" with MATLAB is that it allows you to do some nasty things, such as resizing your matrix in a tight loop. You should really try to pinpoint your bottlenecks using the following command:
profile on
... run your program
profile off
profile report
This will give you nice information about which function takes how long to execute and which line creates the biggest bottleneck. You can also see how many times a function is called and a M-Lint Code Check Report is included.
These measurements and hints can show you the bottlenecks of your algorithm. if your sure there isn't a way to reduce the callcount/speed of a function using a smarter algorithm. Such as do I really need that big 2d matrix where a smart vector would be large enough, or if I found a artifact, why would I still continue searching for artifacts. You could write the functions you're experiencing the most performance problems with in c/c++ and use it as a function in matlab. You can get a big speedup out of correctly choosing which functions to implement in c/c++. There is an amount of overhead with calling a c/c++ function from MATLAB, or more correctly there is a overhead in c/c++ to get the data from MATLAB, so a function which is called 10000 times will not be the best to implement in c/c++, you'd be better of with the function higher up the callstack.
It depends on what your requirements are.
The advantage of using matlab is that it's strong in numerical calculations. If you don't need that, then there is no advantage to using matlab. In this case, all those languages are okay, and many others (Python, C#, ...) as well. It depends on which language you are most comfortable with.
If you do want the advantages of matlab then:
Try optimizing in matlab. Most optimization techniques are language independent.
There are tools to translate matlab to C automatically. You can then try to compile with all optimizations on. I seriously doubt this will help much, however, especially considering the GUI part.
First and foremost, as other answers have mentioned, you need to profile your code to find out where the bottleneck is. I would check out Doug Hull's blog at The MathWorks, specifically this entry about using the profiler. This will help you find out where all the work is being done in your code.
If the source of the slowdown is associated with data processing, there may be a number of ways to speed things up (vectorizing, writing a mex file, etc.).
If the source of the slowdown is your GUI, this may be even easier to solve. There are a number of blog posts, both from Doug and other MathWorkers, which I've seen that deal with GUI design. There have also been a few questions on SO dealing with it (here's one). If you're dealing with displaying very large data sets, this submission from Jiro Doke on The MathWorks File Exchange may help speed things up.
It's hard to give you more specific advice since I don't know how you are designing your GUI, but if that turns out to be the bottleneck in displaying your data there are many resources to turn to for improving its speed before you go through the hassle of switching to a whole other language.
Don't forget that you can create functions in C++ that can be called from Matlab. And TADA, you have access to both environments !
I would use C#. It is easier than C++ and integrates well with the Windows platform. Just find a free graphing library for it and you're good to go.
There are plenty of other options depending on your preference of language. Eg. Qt with Python or C++.
As far as I know, the most common methodology is to first do the proof of concept or just the main algorithm on Matlab, because of its ease of use and convenience for math calculations, and after that to translate it to a "real" programming language in order to improve the performance. Usually C or C++ act as the "real" language, but in your case, aiming to do a Windows application, perhaps C# will be the best option.
I found that GUI programming in MATLAB can get really nasty if your application gets more complex. BTW MATLAB can also be called from Java easily (and vice versa, current versions basically provide an interactive Java console).
Just as a side note, if you still need the math power of Matlab, you may want to check out Scilab. It's open-source and free, and it has examples of how it can be integrated with other C# or C++. I have created projects on which Scilab was running in the background to perform all the data math operations; and displaying them with C#'s ZedGraph library. Worked like magic!
I suggest you using Java and the JFreeChart (http://www.jfree.org/jfreechart/) library. I found very easy (and fast) developing applications with a lot of charts of different typologies. If you don't need particularly fast performances, you can use Java. I suppose that there are similar libraries for C#, but I'm not sure.
An alternative to Matlab and Scilab is another free software: Octave.
I don't know about Scilab, but Octave syntax is nearly the same as matlab so you can import code with minimal effort.
If you need fancy toolboxes though, Scilab and Octave might let you down, so check this.
You can execute Octave functions in a C++ program:
http://en.wikipedia.org/wiki/GNU_Octave
I do not think that you can call your own m-files functions from your C++ program though. In the past, the Matlab compiler would let users run matlab programs without installing Matlab, but not without installing a huge library (250 MB if I remember correctly). Nevermind if your Matlab program took 20 kB, you had to distribute the huge library.
Please someone edit/comment on the situation today!
It has been a while since I used the GUI "ability" of Matlab, but back then (2005) I found it awful. Ugly, hard to use, very hard to maintain, dependent on user settings of windows parameters.
Please comment or edit on that too, they may have made progress!
If they have not, I believe that Matlab is NOT the way to go for a program that you want to deliver to anyone.
If you can use Visual Studio for doing your GUI, do that. I second the earlier opinions: go with what you're comfortable with.
If you need the Matlab functions, go with what you're comfortable with, that supports Matlab libraries.
First of all Visual C++ is not a language is an IDE for developing applications.
Second... Which languages do you know? You can have several options. Take a look to:
C++ + Qt (Mine preferred option, powerful and easy to understand)
C# + .NET or WPF
Java
If you can tell more information we could find a language that matches your needs.
I just heard from somewhere that for numerical computation, "MATLAB does offer some user-friendly APIs. If you call these APIs in your C/C++ code, you can speed up computation dramatically."
But I did not find such information in MATLAB documents like http://www.mathworks.com/support/tech-notes/1600/1622.html and http://www.mathworks.com/access/helpdesk/help/techdoc/matlab_external/bp_kqh7.html. All I learned from these websites is that MATLAB can be called in C and C++ by Matlab engine or by compiling M-files into libraries by mcc. They don't mention any built-in numerical MATLAB APIs that can be called in C/C++.
Can someone please clarify?
Thanks and regards!
You want the "Engine" routines. This allows you to start up a background MATLAB process from C and execute calculations on it: relevant MATLAB documentation.
It works pretty well, have a look at the examples. I would say the most annoying thing getting it working is marshaling the data between C and MATLAB. But that's always a problem when doing this kind of thing.
It sounds like you're looking for the code generation tools in the embedded matlab toolbox or real time workshop.
Do doc eml and look for a the LMS (least mean square) equalizer demo.
The code generator is quite good, it will give you a make file that will build a static library. It's easy to use with your stand alone C/C++ code.
There could be a few things that quote is referencing, I assume that it is referring to the MATLAB Compiler. So going from MATLAB -> C++ you can use the compiler to build standalone "faster" applications. However, when speed testing the improvement, I've noticed it to be negligible. Honestly, you're probably far better off coding your work in C from the get-go, the code that the compiler generates is spaghetti and non-object oriented. I should also mention that this is an expensive extension to Matlab.
You can use the MCR in your own c++ project as a stand-alone library (details)... but you might get similar results using Numerical Recipes.
Disclaimer: I used this product 2-3 years ago, things could be different now.