Is it possible to load the matrix in PETSc binary format from external file at runtime with use of Octave C++ API? I've found the Doxygen documentation, but I can't find anything useful among so many items.
Usually I use "PetscBinaryRead.m" when I want to load a PETSc matrix to Octave, but now in C++ I'm really completely lost.
the PetscBinaryRead.m is not part of Octave, we don't know where you got it or even what it does. You can:
reimplement it on C++, C, or Fortran (only you know what it does)
start the Octave interpreter in your C++ and call PetscBinaryRead from there (see the Octave manual on how to create standalone programs or calling Octave Functions from Oct-files
Related
I wrote a TCPIP-Socket-Connection with Server and Client in C++, which works quite nice in VisualStudio. Now I want to use the C++ - Client in MATLAB/Simulink through MEX-Files and later in a S-Function.
I found two descriptions about MEX-Files.
C++ MEX File Application Just for C++
C/C++ MEX Files C/C++
Now I am confused, which one would be the one to take. I wrote some easy programms with the second, but always got into problems with datatypes. I think, it is because the given examples and functions are only for C and not for C++.
I appreciate any help! Thank you very much!
The differences:
The C interface described in the second link is much, much older (I used this interface way back in 1998). You can create a MEX-file with this interface and have it run on a large set of different versions of MATLAB. You can use it from C as well as C++ code.
The C++-only interface described in the first link is new in MATLAB R2018a (the C++ classes to manipulate MATLAB arrays were introduced in R2017b, but the ability to write a MEX-file was new in R2018a). MEX-files you write with this interface will not run on prior versions of MATLAB.
Additionally, this interface (finally!) allows for creating shared-data copies, in-place operations, etc. (the stuff we have been asking for for many years, but they didn't want to put into the old C interface because they worried it would be too complex for the average MEX-file writer).
Another change to be aware of:
In R2018a, MATLAB also changed the way that complex arrays are stored in memory. In older versions of MATLAB, the real and imaginary components are stored in separate memory blocks. In R2018a and on, they are stored in the same memory block, in the same fashion as you would likely use in your own code.
This affects MEX-files! If you MEX-file uses complex data, it needs to read and write them in the way that MATLAB stores them. If you run a MEX-file compiled for an older version of MATLAB, or compile a MEX-file using the current default building options in R2018a, a complex array will be copied to the old storage model before being passed to the MEX-file. A new compile option to the mex command, -R2018a, creates MEX-files that pass the data in the new storage model unchanged. But those MEX-files will not be compatible with previous versions of MATLAB.
How to choose?
If you need your MEX-files to run on versions of MATLAB prior to the newest R2018a, use the old C interface, you don't have a choice.
If you want to program in C, use the old C interface.
If you need to use complex data, and don't want to incur the cost of the copy, you need to target R2018a and newer, and R2017b and older, separately. You need to write separate code for these two "platforms". The older versions can only be targeted with the C interface. For the newer versions you can use either interface.
If you appreciate the advantages of modern C++ and would like to take advantage of them, and are targeting only the latest and greatest MATLAB version, then use the new C++ interface. I haven't tried it out yet, but from the documentation it looks to be very well designed.
I am currently working on a project in C++, and I am actually interested in using Matlab data structures, instead of having to create my own data types (such as matrices, arrays, etc.)
Is there a way to seamlessly use Matlab objects in C++? I don't mind having to run Matlab in the background while my program runs.
EDIT: A starting point is this: http://www.mathworks.co.uk/help/matlab/calling-matlab-engine-from-c-c-and-fortran-programs.html. I will continue reading this.
You can use instead Armadillo C++ maths library; used by NASA, Boeing, Siemens, Deutsche Bank, MIT, CMU, Stanford, etc.
They have good documentation and examples if you are more familiar with MATLAB/OCTAVE
http://arma.sourceforge.net/docs.html#syntax
I would prefer using native C++ library of some sort and not Matlab. This is likely to be faster for both development and execution.
From writing C++ extensions for Matlab I learned one thing: Using Matlab objects in C++ is likely to give you considerable headache.
Matlab data structures are not exposed as C++ classes. Instead, you get pointers that you can manipulate with C-like API functions.
I recommend to use a native C++ library such as Eigen3.
The functionality you are looking at is not really intended to be used as seamless objects. In the past when I have used it I found it much simpler to do the C parts using either native arrays or a third party matrix library and then convert it into a Matlab matrix to return.
Mixing Matlab and C++ is typically done in one of two ways:
Having a C++ program call Matlab to do some specialist processing. This is chiefly useful for rapid development of complex matrix algorithms. You can do this either by calling the full Matlab engine, or by packaging you snippet of Matlab code into a shared library for distribution. (The distributed version packages a distributable copy of the Matlab runtime which is called with your scripts).
Having a Matlab script call a C++ function to do some specialist processing. This is often used to embed C++ implementations of algorithms (such as machine learning models) or to handle specific optimizations.
Both of these use cases have some overhead transferring the data to/from Matlab.
If you are simply looking for some matrix code to use in C++ you would be better off looking into the various C++ matrix libraries, such as the one implemented in Boost.
You can do mixed programming with C++ and Matlab. There are two possible ways:
Call MATLAB Engine directly: Refer to this post for more info. Matlab will run in the background.
Distribute MATLAB into independent shared library: check out here on how to do this (with detail steps and example).
Is there's away to convert the built-in functions that doesn't have a .m file to C++
I'm read in some paper that neither the Matlab compiler nor the Matlab coder could convert it
so I'm wondering those seem to be the most basic functions is there's another way to convert it or perhaps a C++ library with its equivalent
Check the Boost C++ Library (which also contains ode solvers and many other things) or LAPACK (for linear algebra operations).
For deployment solutions, MathWorks publishes lists of supported toolboxes and functions by each product: MATLAB Coder and MATLAB Compiler
To call MATLAB code in C or C++, how do you choose between using the MATLAB engine and using the MATLAB Compiler mcc to create C or C++ shared libraries from your MATLAB code? What are their pros and cons? For the second method, see http://www.mathworks.com/access/helpdesk/help/toolbox/compiler/f2-9676.html
Are there other ways to call MATLAB from C or C++?
If the computation is linear and long, I would use mcc to compile the code. It is as if MATLAB was simply another library with numerical routines in it to be linked into your program.
If I wanted to provide interaction with MATLAB in my program, where the user could specify any of a large number of statements that would be impossible or merely tedious to code individually, then I would use the MATLAB engine. It is as if I wanted to run MATLAB without the Mathworks' UI.
I have never bothered with opening the MATLAB engine outside of a test.
I have some code which I need to code in C++ due to heavy reliance on templates. I want to call this code from MATLAB: basically, I need to pass some parameters to the C++ code, and have the C++ code return a matrix to MATLAB. I have heard this is possible with something called a MEX file which I am still looking into. However I am not sure what is supported in these MEX files. Is all of C++ (e.g. STL and Boost) supported? How difficult is it?
EDIT: I don't need any shared libraries, just header-only stuff like shared_ptr.
Have a look at the MEX-files Guide, especially Section 25–27 for C++.
The basic STL/Boost data structures should work, but threading with Boost could be a problem.
cout will not work as expected in C++, mexPrintf has to be used instead.
It's certainly possible to write C++ MEX files which use STL and boost. In general, you should be able to do anything you please inside a C++ MEX file. The main practical restriction is that MATLAB already ships with a bunch of libraries, so if you're using one of the boost pieces that needs a shared library (some are header-only), you'll need to match the version you compile against with that shipping with MATLAB.
For instance, MATLAB R2009b ships with boost 1.36 (you can tell by looking at the names of the libraries in <matlabroot>/bin/<arch>).
The C++ files are actually compiled by an external compiler. Use mex -setup to select which one (here is a list of supported compilers). Therefore, you shouldn't have too many weird things happen, nor should you be too restricted by what you can do.
I did some MEX stuff last year, and my memory is a bit rusty, but you do need to construct MATLAB arrays using MEX functions. I found the MATLAB documentation adequate, and the whole experience not too painful.
STL is definitely supported. Boost probably yet. The point is as long you have your STL and BOOST deployed on your computer, you should be good to go.