timestwo.c



#include "mex.h"

void timestwo (double y[ ], double x[ ], int i)
{
  	int j;
  	for (j = 0; j < i; j++)
    		y[ j ] = 2.0 * x[ j ];
}

void mexFunction (int nlhs, mxArray *plhs[ ], int nrhs,const mxArray, *prhs[ ])
{
  	double *x, *y;
  	int        mrows, ncols;
  
  	/* The input must be a noncomplex scalar double */
  	mrows = mxGetM (prhs[ 0 ]);
  	ncols  = mxGetN (prhs[ 0 ]);
   	 
  	/* Create matrix for the return argument */
  	plhs[ 0 ] = mxCreateDoubleMatrix (mrows, ncols, mxREAL);
 	 
  	/* Assign pointers to each input and output */
  	x = mxGetPr (prhs[ 0 ]);
  	y = mxGetPr (plhs[ 0 ]);
 	 
  	/* Call the timestwo subroutine */
  	timestwo (y, x, ncols);
}

Here's how you'd compile and run it:

» mex timestwo.c
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 11.00.7022 for 80x86 
Copyright (C) Microsoft Corp 1984-1997. All rights reserved. 

» timestwo(7)
ans =
    14

» timestwo([7, 3])
ans =
    14     6

Explaining "timestwo.c"

The C-MEX function "timestwo" has the following pseudo-code:


#include "mex.h"
void timestwo (double output_vector, double input_vector, int length_of_input_vector)
{
  	output_vector = input_vector  * 2
}

void mexFunction (int nlhs, mxArray *plhs[ ], int nrhs,const mxArray, *prhs[ ] )
{
  	double *x, *y;
  	int        mrows, ncols;
  
  	/* Get the dimensions of input matrix */
  	mrows = number of rows in input matrix
  	ncols   = number of columns in input matrix
    
  	/* Create matrix to hold the output */
  	plhs[ 0 ] = a real, double matrix of size mrows x ncols 
  
  	/* Assign pointers to each input and output */
  	x = pointer_to_input
  	y = pointer_to_output
  
  	/* Call the timestwo subroutine */
  	timestwo (y, x, ncols);
}