Hi and many thanks for your answer.
The answer is that  when I write the code:>>which mex 
the output is:
C:\Program Files\MATLAB\R2012a\toolbox\matlab\general\mex.m
Instead, when I write the code:>> mex -setup
the output is:
Welcome to mex -setup.  This utility will help you set up 
a default compiler.  For a list of supported compilers, see  
http://www.mathworks.com/support/compil ... win32.html  Please choose your compiler for building MEX-files:  
Would you like mex to locate installed compilers [y]/n? y 
Select a compiler: 
[1] Lcc-win32 C 2.4.1 in C:\PROGRA~1\MATLAB\R2012a\sys\lcc  
[0] None  
Compiler: 1 
Please verify your choices:  
Compiler: Lcc-win32 C 2.4.1 
Location: C:\PROGRA~1\MATLAB\R2012a\sys\lcc  
Are these correct [y]/n? y 
Trying to update options file: C:\Users\oana\AppData\Roaming\MathWorks\MATLAB\R2012a\mexopts.bat 
From template:              C:\PROGRA~1\MATLAB\R2012a\bin\win32\mexopts\lccopts.bat  
Done . . .  
************************************************************************** 
  Warning: The MATLAB C and Fortran API has changed to support MATLAB 
           variables with more than 2^32-1 elements.  In the near future 
           you will be required to update your code to utilize the new 
           API. You can find more information about this at:            
http://www.mathworks.com/help/techdoc/m ... nue-1.html            Building with the -largeArrayDims option enables the new API. 
**************************************************************************
Thanks in advance for your support!