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//---Inside mexFunction---
//DeclarationsmxArray *zData;
int Num;//Copy input pointer z
zData = prhs[2];
//Get the IntegerNum = (int)(mxGetScalar(zData));
//print it out on the screenprintf("Your favorite integer is: %d",Num);
Three data types have been shown here. There are several others and the MATLAB help as well as the MATLAB example code shows how to use them. Now to export the data....
Assigning return values and data to the left hand side parameters is very similar to getting the data from the last section. The difference here is that memory must be allocated for thedata strucure being used on the output. Here is an example of how to return a 2-D matrix. This code will take the input x and return a copy of the matrix to z0 with every point in x multiplied by 2.Note that I am not copying the name of the output mxArray pointer into another variable.
//---Inside mexFunction---
//DeclarationsmxArray *xData;
double *xValues, *outArray;int i,j;
int rowLen, colLen;//Copy input pointer x
xData = prhs[0];
//Get matrix xxValues = mxGetPr(xData);
rowLen = mxGetN(xData);colLen = mxGetM(xData);
//Allocate memory and assign output pointerplhs[0] = mxCreateDoubleMatrix(colLen, rowLen, mxREAL); //mxReal is our data-type//Get a pointer to the data space in our newly allocated memory
outArray = mxGetPr(plhs[0]);
//Copy matrix while multiplying each point by 2for(i=0;i<rowLen;i++)
{for(j=0;j<colLen;j++)
{outArray[(i*colLen)+j] = 2*xValues[(i*colLen)+j];
}}
While it may be nice to write functions in C, there are so many useful and fast pre-written functions in MATLAB that it would be a crime if we could not use them. Luckily,The Mathworks (creators of MATLAB) has provided this capability. Built-In functions have a parameter list similar to the mexFunction itself. This example uses the built-in function z = conv(x,y);
//---Inside mexFunction---
//DeclarationsmxArray *result;
mxArray *arguments[2];
//Fill in the input parameters with some trasharguments[0] = mxCreateDoubleMatrix(1, 20, mxREAL);arguments[1] = mxCreateDoubleMatrix(1, 10, mxREAL);//In the real world I imagine you would want to actually put
//some useful data into the arrays above, but for this example//it doesnt seem neccesary.
//Call the FunctionmexCallMATLAB(1,&result,2,arguments,"conv");
//Now result points to an mxArray and you can extract the data as you please!
Compiling the MEX-Files is similar to compiling with gcc or any other command line
compiler. In the MATLAB command prompt, change your current directory to thelocation of the MEX source file. Type:
mex filename.c
into the MATLAB
command window. MATLAB may ask you to choose a compiler. Choose the compiler with MATLAB in its directory path.Your function will be called with the same name as your file. (ex:
mex jasonsFunction.c
produces a function that can be called from MATLAB as
[z0,z1] = jasonsFunction(x,y,z);
)
After compiling MATLAB produces the actual MEX binary that can be called as a normal MATLAB function. To call this function, you must be in the same directory with the binary. The binary goes by different namesdepending what system you compiled the source on (ex: Windows=.dll MacOSX=.mexmac Solaris=.mexsol Linux=.mexlx). Your MEX-function will have to be compiled on each type of system that you want to run it on because thebinaries are operating system specific.
Here is a nice list of useful functions in the mex library that make life a lot easier. Most of these work in similar fashion to those functions described above. The full list can be found inthe MATLAB help documentation with many examples. There are also some example files in the MATLAB extern directory (MATLAB/extern/examples/mx or mex).
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