Segmentation fault in c - probably connected with pointers

When I add this function in my program, I get this error: "Segmentation fault". I have found that it is probably connected with pointers.

This is my function:

void deBoor(double* D, double* t, double x, int k, int n, double* R){   int i,j,l;   double ret[3];   double* P=(double*)malloc(n*sizeof(double));   for(i=0; i<n; ++i) P[i]=D[i];   j=k;   while(x<t[j]) ++j;   while(x>=t[j+1]) ++j;   for(l=1; l<=k; ++l){       for(i=j; i>=j-k+l; --i)       {          P[i]=(x-t[i])/(t[i+k+1-l]-t[i])*P[i]+(t[i+k+1-l]-x)/(t[i+k+1-l]-t[i])*P[i-1];       }   }   R[0]=P[j];   free(P);}

And this is the call of the function:

deBoor (kontrolne_tocke, prosirena_particija, xx, k, duljina, R);