/************************************************************
* ROOT macro to calculate moments (reads from file data.dat)
*
* Note: function with the same name as the source code
*       can be executed in ROOT just by '.x upf_cv4_mom.cc'
*       or from terminal by 'root upf_cv4_mom.cc'
*
*       Optionally, source file name can be specified in 
*       the function argument: '.x upf_cv4_mom.cc("NAME")'
*       If it is not specified, 'data.dat' is used.
************************************************************/

// main function:
int upf_cv4_mom(const char* fName = "data.dat")
{
	// settings:
	const int nData = 1200;		// max. number of lines in data.dat

	double x[nData];	// declaration of an array (size = nData)
	double mean   = 0;	// mean = 1/N sum_i x_i
	double sigma2 = 0;	// sigma^2 = 1/(N-1) sum_i (x_i - mean)^2

	FILE *fin;				// input file descriptor
	fin = fopen(fName,"r");	// open for reading
	if (fin == NULL)
		return 1;		// if the file could not be open

	int N;				// number of lines read
	for (N = 0; N < nData; N++)
	{
		// This fscanf reads one double precision number from one line
		// It returns the number of successfully read numbers, i.e. 1 or 0
		if (fscanf(fin,"%lf",&x[N]) != 1)
			break;
		mean += x[N];
	}
	fclose(fin);
	printf("Read %i lines from %s.\n",N,fName);
	mean /= N;
	printf("mean = %f\n",mean);

	for (int i = 0; i < N; i++)
		sigma2 += pow(x[i] - mean, 2);

	sigma2 /= (N - 1);

	printf("standard deviation = %f\n", sqrt(sigma2));

	return 0;
}