Thread: Arrays, pointers, trouble..

Hi all!

I am trying to write a Matlab mex-file, and I find the c-coding part a bit challenging. I can get the code below to compile, but it doesn't do what is expected:

Code:

#include <math.h>
#include "mex.h"



/*Subroutine to calculate the Fuzzy Sample Entropy*/
void FSE(double *cop, int M, double r, double c, mwSize N, double *FuzzSampEnt) {
    
    mwIndex m, i, ii, j, jj, k, l;
    double expo, d, *seg_i, *seg_j, count, sumCim, *Cim, CIM[2];
 
    expo=(log(log(pow(2, c)))/log(r));    
   
    
    for (m=M;m<M+2;m++) {
        
        seg_i=mxCalloc(m, sizeof(double));
        seg_j=mxCalloc(m, sizeof(double));
        Cim=mxCalloc(N-m, sizeof(double));
        
        for (i=0; i<N-m; i++) {
            count=0;            
                      
            for (ii=0; ii<m; ii++){
                seg_i[ii]=cop[i+ii];//TROUBLE
            }
            
            for (j=0; j<N-m; j++) {
                
                for (jj=0; jj<m; jj++) {
                    seg_j[jj]=cop[j+jj];//TROUBLE
                }
   
                d=0;
                /*Finding the maximum absolut value of seg_i-seg_j*/
                for (k=0; k<m; k++) {
                    if (d < fabs(seg_i[k]-seg_j[k])) {
                        d=fabs(seg_i[k]-seg_j[k]);
                    }
                }
                
                /*if d=0, self match*/
                if (d>0) {
                    count+=exp(-(pow(d, expo/c)));
                }
                
            }
            Cim[i]=count/(N-m-1);
        }
        
        sumCim=0;
        for(l=0;l<N-m;l++){
            sumCim+=Cim[l];
        }
        
        if (m==M){
            CIM[0]=sumCim/(N-m);
        }
        else if (m==M+1){
            CIM[1]=sumCim/(N-m);
        }
        
    }
    
    *FuzzSampEnt=seg_j[k];//-log(CIM[1]/ CIM[0]);
    
    mxFree(seg_i);
    mxFree(seg_j);
    mxFree(Cim);

}


/*the gateway function*/
void mexFunction(int nlhs, mxArray *plhs[ ],
        int nrhs, const mxArray *prhs[ ]) {
    
    int M;
    double *cop, *FuzzSampEnt;
    double c, r;
    mwSize N;
    
    if(nrhs!=4) {
        mexErrMsgTxt("Four inputs required (cop,M,r,c).");
    }
    
    /*Assign pointers*/
    cop=mxGetPr(prhs[0]);
    N=mxGetM(prhs[0]);
    M=(int)(mxGetScalar(prhs[1]));
    r=mxGetScalar(prhs[2]);
    c=mxGetScalar(prhs[3]);
     
    plhs[0] = mxCreateDoubleMatrix(1, 1, mxREAL);
    FuzzSampEnt = mxGetPr(plhs[0]);
    
    /*Call the subroutine */
    FSE(cop, M, r, c, N, FuzzSampEnt);

    return;
}

The trouble seems to be here: seg_i[ii]=cop[i+ii]; cop[i+ii] seems to be what it should be, but I can't seem to get it's value to seg_i[ii]. Also I'm not sure if it is necessary to use pointers here at all. I know that seg_i and seg_j are either M or M+1 in length and Cim is either N-M or N-M-1 in length.

The idea would be to make the code as fast as possible, as fast as possible.. So how would you deal with the seg_i, seg_j and Cim? Can you see what I'm doing wrong in here?

Thank You!

-Aino

Well, probably the real problem is earlier than in this point, but until this point I get the stuff out what I want. I have changed the ending of the code, the output parameter FuzzSampEnt to see what it gives out at what point (I'm sure there is a better way). So it would seem that for example FuzzSampEnt=expo; or FuzzSampEnt=cop[ii+i]; give out what they are supposed to, but *FuzzSampEnt=seg_i[k], gives out something funny like -9*10^303. The true output, -log(CIM[1]/ CIM[0]), is commented, but using it the function gives out NaN.