import java.util.Random;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.io.*;

public class NNUtils {

	public static float[][] multiply(float[][] a,float[][] b){
	// multiply two matrices and return the result
	// the order of the algorithm is n^3

		if( a[0].length != b.length ){
			System.err.println("error: inner matix dimentions must agree");
			return null;
		}
		float[][] result = new float[a.length][b[0].length];
		for(int i=0; i < a.length; i++)
			for(int j=0; j < b[0].length; j++){
				float sum = 0.0f;
				for(int k=0; k < b.length; k++)
					sum += a[i][k]*b[k][j];
				result[i][j] = sum;
			}
		return result;
	}

	public static float[][] random_matrix(int rows,int cols,float min,float max){
	// create a rows by cols matrix of random values in range [min,max]

		Random rand = new Random();
		float[][] result = new float[rows][cols];
		for(int i=0; i < rows; i++)
			for(int j=0; j < cols; j++)
				result[i][j] = rand.nextFloat() * (max - min) + min;

		return result;
	}

	public static String array2string(float[] n){

		String s = "[";
		for(int i=0; i < n.length - 1; i++)
			s += n[i]+", ";
		s += n[ n.length - 1 ]+"]";
		return s;
	}

		public static float[][] read_training_set(String file_name){
	// Read the training set from file_name, and return it in the
	// form of a matrix.
	// Each line of file_name is a comment (started with //) or
	// otherwise specify a training vector (we don't know how many
	// of elements of such a vector are inputs and outputs)

		float[][] matrix; // the training set matrix

		BufferedReader inp;
		try{
			inp = new BufferedReader(new FileReader(file_name));

			String s;
			ArrayList line = new ArrayList();
			while( (s = inp.readLine()) != null ){
				ArrayList fn = new ArrayList(); // to hold float numbers in a line
				StringTokenizer st = new StringTokenizer(s,", \t",false);
				if( ! st.hasMoreTokens() )
					continue;
				String token = st.nextToken();
				if( token.equals("//") )
					continue;

				fn.add(new Float(Float.parseFloat(token)));
				while( st.hasMoreTokens() ){
					token = st.nextToken();
					fn.add(new Float(Float.parseFloat(token)));
				}
				line.add(fn);
			}

			int rows = line.size();
			matrix = new float[rows][];

			for(int i=0; i < rows; i++){
				ArrayList fn = (ArrayList)line.get(i);
				matrix[i] = new float[fn.size()];
				for(int j=0; j < fn.size(); j++)
					matrix[i][j] = ((Float)fn.get(j)).floatValue();
			}
		}catch(Exception ex){
			System.err.println("error in "+file_name);
			return null;
		}
		try{
			inp.close();
		}catch(Exception ex){ System.err.println(ex); }

		return matrix;
	}

  public static void main(String[] args) {

	System.out.println("START...");
	float[][] a = NNUtils.random_matrix(100,100,-1,1);
	float[][] b = NNUtils.random_matrix(100,100,-1,1);
	
	long l1 = System.currentTimeMillis();
	float[][] c = NNUtils.multiply(a,b);
	long l2 = System.currentTimeMillis();
	System.out.println((l2-l1)/1000+" sec");
  }
}