Realization of the code for calculating the mean square error of GPS Height Fitting

Don't talk much , Go straight to the code ,c Code

				// 2.1、 Use the median method , Instead of arithmetic median 
				qsort(tmp_v_res, ns, sizeof(double), cmpres);
				median_v_res =median(tmp_v_res, ns);//  Mean value of observation    Eq.14
				
				// 2.1.1  Find the deviation , Centralization 
				for (j = 0; j < ns; j++) {
					tmp_v_res[j] -= median_v_res;// Eq.15
					/*v_res[j] -= median_v_res;*/
					if (tmp_v_res[j] < 0) tmp_v_res[j] *= -1;// Take the absolute value 
				}

				// 2.1.2  Use the median to calculate the variance factor 
				qsort(tmp_v_res, ns, sizeof(double), cmpres);
				median_v_res = median(tmp_v_res, ns);// Mean value of observation 
				sigma1 = median_v_res / 0.6745;// Eq.17
				printf(" Robust unit weight mean square error (weighted)sigma1= %f\n", sigma1);


/*  Residual comparison  */
static int cmpres(const void *p1, const void *p2){
	double *q1 = (double *)p1, *q2 = (double *)p2;
	double tt = (*q1) - (*q2);
	return tt<-0.0 ? -1 : (tt>0.0 ? 1 : 0);
}

/*  Find the median  */
static double median(const double* A,unsigned int n){
	if (n>0){
		return (n & 1 == 1) ? A[(n - 1) / 2] : (A[n / 2] + A[n / 2 - 1]) / 2;
	}
	return 0;
	
}