sparse matrix manipulation in matlab mex files

[nitro_n2o]

Hi all,

i'm try to build a sparse matrix in matlab mex file from a data file. I can get the the row, column and value, but the values in the matrix are never written!

can any one help on how to a sparse matrix using a mex files?

Thanks in advance

[kjohansen]

post the code you have so far.

mex allows you to write C functions for use with matlab, so your sparse matrix manip is written in C not mex, mex is not a language. There are some special functions in "mex.h" for access to the inputs and outputs...

[nitro_n2o]

yeah sure i understand

so here is what i do

plhs[0] = mxCreateSparse(100,100,20,mxREAL);
int *ir = mxGetIr(plhs[0]);
int *jc = mxGetJc(plhs[0]);
double *pr = mxGetPr(plhs[0]);

int r, c;
double v;
int k=0;
/* line looks like this: 1 3 32.8 */
while(fgets(line,sizeof line, fp)){
sscanf(line,"%d %d %f",&r,&c,&v);
ir[k] = r;
jc[k] = c;
pr[k] = v;
k++;
}


After that the matrix returned is just All zeros 100x100 sparse

[ubuMike]

Same Problem Here!


//read matrix
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "mex.h"
#include "matrix.h"


struct sparseMtx{
float len;
unsigned int pixel; //0 to 4,294,967,295
unsigned int voxel; //0 to 4,294,967,295
};

void mexFunction(
int nlhs, mxArray *plhs[],
int nrhs, const mxArray *prhs[])
{
char *filename = mxArrayToString(prhs[0]);

int* MNmax = (int*)mxGetData(prhs[1]);

//M pixels N voxels
plhs[0] = mxCreateSparse(MNmax[0],MNmax[1],MNmax[2],mxREAL);
double *sr = mxGetPr(plhs[0]);
int* irs = mxGetIr(plhs[0]);
int* jcs = mxGetJc(plhs[0]);

//get
int lenDim[] = {1,MNmax[2]};
plhs[1] = mxCreateNumericArray(2,lenDim,mxSINGLE_CLASS,mxREA L);
plhs[2] = mxCreateNumericArray(2,lenDim,mxINT32_CLASS,mxREAL );
plhs[3] = mxCreateNumericArray(2,lenDim,mxINT32_CLASS,mxREAL );
float* s = (float*)mxGetData(plhs[1]);
int* ir = (int*)mxGetData(plhs[2]);
int* jc = (int*)mxGetData(plhs[3]);

//open file
FILE *mtxData;
mtxData = fopen(filename,"r");
sparseMtx *matrix;
matrix = new(sparseMtx);

for(int i=0; i<MNmax[2];i++){
fread ( matrix, 1, sizeof(sparseMtx), mtxData );

sr[i] = (double)matrix->len;
irs[i] = (int)matrix->pixel;
jcs[i] = (int)matrix->voxel;

s[i] = matrix->len;
ir[i] = matrix->pixel;
jc[i] = matrix->voxel;

printf("%i\n",irs[i]);
}

fclose(mtxData);
}

The output from s ir and jc show up fine, but the sparse matrix is empty!!!

[ubuMike]

Google compressed-column form

ir and jc must be non-zero and increasing.