#include <iostream>
#include <math.h>
#include <stdio.h>
using namespace std;

float data[1000000][128];

float mean(float *data, int size)
{
	float sum = 0;
	for(int i = 0; i < size; ++i)
		sum += data[i];
	return sum/size;
}

float stdev(float *data, int size, float mean)
{
	float sum = 0;
	for(int i = 0; i < size; ++i)
		sum += (data[i] - mean) * (data[i] - mean);
	return sqrt(sum/(size - 1));
}


void random_walk(int length_rw, int number_rw)
{
	for(int i = 0; i < number_rw; ++i)
	{
		data[i][0] = 0;
		for(int j = 1; j < length_rw; ++j)
		{
			float bias = (float)RAND_MAX / 2;
			data[i][j] = data[i][j - 1] + (float)random() - bias;
		}
	}
}

int main(int argc, char *argv[])
{
	srandom(time(NULL));
	if(argc != 3)
	{
		cerr << "Usage: random_walk length number" << endl;
		exit(1);
	}
	
	int length = atoi(argv[1]);
	int number = atoi(argv[2]);
	random_walk(length, number);
		
	//Normalization
	for(int i = 0; i < number; ++i)
	{
		float mean_i = mean(data[i], length);
		float std_i = stdev(data[i], length, mean_i);
		for(int j = 0; j < length; ++j)
			data[i][j] = (data[i][j] - mean_i)/std_i;
	}

	//Write to the output file
	FILE *outfile;
	outfile = fopen("random_w.dat","w");
	if(!outfile)
	{
		cerr << "Open output file error!" << endl;
		exit(1);
	}
	for(int i = 0; i < number; ++i)
	{	
		for(int j = 0; j < length; ++j)
			fprintf(outfile,"%8f\t", data[i][j]);
		fprintf(outfile,"\n");
	}
		
	return 1;
}