MatLab API in C++

at runtime; computation time can be a little slow
has excellent

prototyping and plotting functionality
contains convenient and very robust matrix operation packages

floating point computation
is non-trivial to produce visual effects in
eg.

plotting, GUIs, nice tables
can be difficult to secure a robust vector algebra package for

in MatLab
plotting, graphing, tables in MatLab
For programmers with a robust

& complex C++ program intending to plot results they are already obtaining
For MatLab programming with scripts which frequently lag

other languages can do it also
Not restricted to the MS

Visual Studio environment the demos are written in
Also possible to invoke a C++ routine from MatLab’s environment

Three ways to interact
Send Data from C++ to MatLab
Call a MatLab function from C++
Generate a Dynamic Link Library (dll) file from a .m file
We will use the first one

v.6.0
MatLab
the demo uses MatLab v.7.0.1
Assume’s prior programming experience in

both MatLab and C++
no explanations are given for the commands
Following slides explain setting up the demonstration program environment

Options
- Directories Tab
- Select "Include files" from the

drop-down list
- Add "C:\MATLAB701\EXTERN\INCLUDE" to the list
- Select "Library Files" from the drop-down list
- Add ”C:\MATLAB701\EXTERN\LIB\WIN32\MICROSOFT\MSVC60“
Library paths vary depending on the language and compiler

library files:

Method 1) - Project -> Settings

- Links Tab
Under "Object/Library Module:", add three file names:
- Libmx.lib
- libmex.lib
- libeng.lib

Method 2) Add the following lines of code just under the
includes in the source code:

#pragma comment( lib, "Libmx.lib" )
#pragma comment( lib, "libmex.lib" )
#pragma comment( lib, "libeng.lib" )

create a pointer to it:

Engine *m_pEngine;
m_pEngine = engOpen(NULL);
if (m_pEngine ==

NULL)
{
cout << "Error: Not Found”
<< endl;
exit(1);
}

= x.^2;“ );
engEvalString(m_pEngine, “plot(x,y);“ );

Enables programmer to invoke

any command in MatLab from the C++ platform (convenient)
Not special by itself - might as well work straight from MatLab

type
Every variable in MatLab is a matrix – for C++

to exchange data with it, a data type that both C++ and MatLab recognize is needed
mxArray can “bundle” C++ variables as matrices, so both platforms recognize this data type

create an mxArray for it
- Allocate the space (mxCreateDoubleMatrix)
-

Copy the value (memcpy)
- Name the variable in the Engine (engPutVariable)

double x[0];
mxArray *m_X;
m_X=mxCreateDoubleMatrix(1, 1, mxREAL);
memcpy((void *)mxGetPr(m_X), (void *)x, sizeof(double)*1);
engPutVariable(m_pEngine, "x", m_X);

Pointer m_pEngine is used to specify the engine
Variable x in the MatLab Engine gets the value of x[0] in C++

it into C++ as a mxArray matrix, then extract the

bundled value out of that mxArray and into a C++ variable

double *cresult;
mxArray *mresult;
mresult = engGetVariable(m_pEngine,"z");
cresult = mxGetPr(mresult);
cout << cresult[0];

mxGetPr returns a pointer to a copy of the double value z stored in the MatLab Engine
Warning: Unpredictable fatal errors occur if the data type in MatLab doesn’t closely resemble the data type in C++ eg. Copying a 3x1 vector into a scalar

parameters of the memory allocation and copy routine to match

the dimensions of the array being passed
Pass a vector a of dimensions: 1 x SIZE

double a[SIZE];
mxArray *A;
// assume a gets initialized, all values
A=mxCreateDoubleMatrix(1, SIZE, mxREAL);
memcpy((void *)mxGetPr(A), (void *)a, sizeof(double)*SIZE);
engPutVariable(m_pEngine, "a", A);

Copies entire C++ array a into the MatLab Engine’s a

x SIZE

double c[SIZE][SIZE];
// assume c gets initialized, all of it

mxArray *mxc;
mxc = mxCreateDoubleMatrix(SIZE, SIZE, mxREAL);
memcpy((void *) mxGetPr(mxc), (void *)c, sizeof(double)*SIZE*SIZE);
engPutVariable(m_pEngine, "c", mxc);
engEvalString(m_pEngine, "c = c';");

Note: C++ has row-major storage, and MatLab has column-major storage. Thus a matrix being exchanged must be transposed, either before or after the exchange, to maintain the matrix’s semantics

in Microsoft Visual Development Studio C++ v.6.0
Demonstrates graph plots, invoking

commands, input, output, and passing vectors and matrices.

Functions from Within A  C/C++ Program
http://prism.mem.drexel.edu/Shah/public_html/c2matlab.htm
Microsoft Visual Studio C++ &

Interfacing Matlab with C/C++, Java
http://www.qcf.gatech.edu/academic/LabDataAccess/C++IntroductionMatLab.Interfacings.doc
MatLab – The Language of Technical Computing, External Interfaces
http://www.mathworks.com.au/access/helpdesk/help/pdf_doc/matlab/apiext.pdf

this presentation.