I have created a sparse matrix in a MEX-file following the example shown in here. Now how do I access this matrix from MATLAB as a whole.
#define NZMAX 4
#define ROWS 4
#define COLS 2
int rows=ROWS, cols=COLS;
mxArray *ptr_array; /* Pointer to created sparse array. */
static double static_pr_data[NZMAX] = {5.8, 6.2, 5.9, 6.1};
static int static_ir_data[NZMAX] = {0, 2, 1, 3};
static int static_jc_data[COLS+1] = {0, 2, 4};
double *start_of_pr;
int *start_of_ir, *start_of_jc;
mxArray *array_ptr;
/* Create a sparse array. */
array_ptr = mxCreateSparse(rows, cols, NZMAX, mxREAL);
/* Place pr data into the newly created sparse array. */
start_of_pr = (double *)mxGetPr(array_ptr);
memcpy(start_of_pr, static_pr_data, NZMAX*sizeof(double));
/* Place ir data into the newly created sparse array. */
start_of_ir = (int *)mxGetIr(array_ptr);
memcpy(start_of_ir, static_ir_data, NZMAX*sizeof(int));
/* Place jc data into the newly created sparse array. */
start_of_jc = (int *)mxGetJc(array_ptr);
memcpy(start_of_jc, static_jc_data, NZMAX*sizeof(int));
/* ... Use the sparse array in some fashion. */
/* When finished with the mxArray, deallocate it. */
mxDestroyArray(array_ptr);
Also while storing the values in static_pr_data, ic_data and jc_data is it necessary to store the values in column major format? Is it possible to store in row major format (since it will speed up my calculation)?
In the example you link to, the last statement is
mxDestroyArray(array_ptr);
Instead of destroying the array, you need to return it as the output of your MEX-function. Your MEX-function C/C++ source code should have a function named mexFunction (the entry point for the MEX-function) that looks like this:
void mexFunction(int nlhs, mxArray * plhs[], int nrhs, const mxArray * prhs[])
To return an output from the MEX-function, assign it into the plhs array, like this:
plhs[0] = array_ptr; // instead of mxDestroyArray(array_ptr);
Compile the code into a MEX-function (Let's call it sparsetest). Invoke it from MATLAB like this:
>> output = sparsetest;
Now output is a MATLAB variable containing the sparse matrix you created in your MEX-function.
As for storing the data in row-major format, that is not possible. MATLAB only handles column-major sparse matrices.