A class wrapper for Matlab(c) ActiveX Control

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Introduction

Matlab(c) is a well-known scientific software covering a wide range of engineering and mathematicals fields. It contains also a set of complete and powerfull visualization tools.

Matlab(c) contains it's own language and you can easily develop applications on it. However, sometimes you will want to run it from a C/C++ application and that's where everything get's tricky. In fact, although Matlab(c) comes with a C API, it is complicated to use: linking problems, compiler special flags and other mysterious bugs (maybe I did it all wrong).

Another solution is to use the COM interface of the ActiveX control. The sad thing about this interface is that... it's COM and you end up with dozens of lines of code... That's where the CMatlabEngine gets in the play. It hides all the COM code (getting CLSID, getting IDispatch, allocating variants, setting function arguments and many others) and enables you to focus on the main part of the job: use Matlab(c).

This article will discuss the main features the class, for further details check the Doxygen documentation that is shipped with the demo project. Note that you can also generate it by running Doxygen on MatlabEngine.h

Initializing the engine

All the initialization code is contained in the constructor of CMatlabEngine. You can check that the server has been correctly initialized by calling IsInitialized:

// Initializing COM
CoInitialize(NULL);

...
// Hooking matlab engine
CMatlabEngine mt;
if (!mt.IsInitialized())
   // could not initialize matlab engine, do something about it

Do not forget to uninitialize COM when quitting the application:

CoUninitialize();

Engine main methods

The matlab engine contains 5 main methods: Execute, PutMatrix, GetMatrix, PutString and GetString

Executing Matlab(c) code:

You can execute Matlab(c) code by calling Execute( LPCTSTR szMatlabCode ):

// this code will show the classic Matlab(c) demo
mt.Execute(_T("surf(peaks)"));
mt.Execute(_T("title('demo')"));

Sending arrays to Matlab(c)

You can send array, real or complex, in the form of vector to Matlab(c) by using PutMatrix.Note that the vector in PutMatrix have to be ordered line by lines: for a matrix M of size (mxn), M(i,j) is equivalent to M[i* n + j].

UINT nRows=10; // number of rows
UINT nCols=2;  // number of columns
vector<double> v( nRows * nCols );
// filling up v
...
// sending v to Matlab(c) with name "Mv"
mt.PutMatrix( _T("M"), v, nRows, nCols);
// M is now a matrix in the Matlab(c) workspace

Retreiving arrays from matlab

You can retreive arrays (real or complex) by calling GetMatrix( It is the dual of PutMatrix):

mt.Execute(_T("v=[1 2 3; 4 5 6]';"));
vector<double> vReal;
UINT nRows, nCols;
mt.GetMatrix(_T("v"), nRows, nCols, vReal);	

nRows and nCols now contains the dimension of the array and vReal the data.

Sending string to Matlab(c)

Piece of cake using PutString:

   mt.PutString("text", "Inserting a string named text");

Getting string from Matlab(c)

Use the method GetString:

LPTSTR szText;
// we suppose that myText is a string variable in Matlab
mt.GetString("myText",szText);

Note that szText is allocated on the heap by GetString, the memory cleaning is left to the user.

Workspace

You can modify the workspace you are working on by using SetWorkspace. By default, the workspace is "base". If you want to declare global variables, use "global" workspace.

Handling the Matlab Window state

• Minimize the command window,

  mt.MinimizeWindow();
  

• Maximize the command window,

  mt.MaximizeWindow();
  

• Show, hide the command window,

  mt.Show( true /* true to make it visible, false to hide it*/);
  

• Get the visibility state the command window,

  if(mt.IsVisivle())
      // Matlab is server is visible...
  

• Quit the command window,

  mt.Quit();
  

Known bugs and limitations

Matlab 5.3 and earlier

Some function interface from the Matlab engine have been introduced only with the version 6.0 therefore user with version earlier than 6.0 would have faced problem with the class.

If you have a Matlab earlier than v6.0, undefine the MATLAB_VERSION_6 constant that is at the beginning of MatlabEngine.h, it will disable the following functions: IsVisible, Show, PutString, GetString

Further developments

• Write PutCellArray and GetCellArray to write and read cell arrays.

Reference and further reading

• Matlab(c) External API reference, pg 323-328
• Matlab application engine type library file (mlapp.tlb) in bin/win32 can give you the available methods implemented in the interface.

Revision History

21-10-2002	Added references
10-09-2002	GetString is now working! At last ! Fixed bugs in GetResult, GetMatrix thanks to Juan Carlos Cobas.
09-25-2002	GetMatrix is now working! At last !
09-23-2002	Added PutString method Added MATLAB_VERSION_6 string for Matlab version < 6. Thanks for ZHANG Yan for finding the workaround.