1. ENERGY 211 / CME 211
Lecture 28
December 1, 2008

2. Calling C/C++ from MATLAB
A MEX-file is a C or FORTRAN program that can be called from MATLAB
It is a dynamic-link library that implements a single MATLAB function
Name of library (minus extension) is name of MATLAB function
Most useful to allow existing compiled-language applications to be used from within MATLAB without having to rewrite code

3. MATLAB Arrays A MATLAB variable is stored in a mxArray
An mxArray contains info about a variable's type, size, etc. and its data
Internally, matrices are stored in column-major order, like in FORTRAN
For complex data, real and imaginary parts are stored in separate arrays
Strings are stored as arrays of unsigned integers, not characters

4. The Interface
The code for your MEX-file must include a function called mexFunction, which is called by MATLAB
It takes these arguments:
int nlhs: number of output arguments
mxArray *plhs[]: array with nlhs elements that point to output arguments
int nrhs: number of input arguments
const mxArray *prhs[]: array with nrhs elements that point to input arguments

5. Working with Arguments
mxGetPr returns a pointer to the real part of an input or output argument
If argument is complex, use mxGetPi to get pointer to imaginary part
mxGetM, mxGetN return the size of a matrix passed as an argument
mxGetScalar returns the value of a scalar argument, as a double
mxCreateDoubleMatrix allocates a matrix for an output argument

6. Building MEX-files in MDS
Project: "Win32 Dynamic-Link Library"
Change Project Settings:
Compile tab: add include directory from MATLAB installation where mex.h is found
Link tab: change Output file name extension from .dll to .mexw32; add mx and mex to list of Libraries; add location of MATLAB's .dll under Additional Library Path
Place library in directory from which it will be run in MATLAB

7. Calling MATLAB from C/C++
Must #include "engine.h" and link with eng library
engOpen function starts MATLAB
engEvalString evaluates MATLAB command in string s
engGetVariable gets variable from MATLAB workspace and stores mxArray
engPutVariable puts mxArray in MATLAB workspace with given name

8. Next Time Calling FORTRAN from C/C++ code And vice versa
Using command-line arguments