package cn.edu.bjut.chapter5;

public class Matrix {
	private double[][] values;
	private int nrows, ncols;

	public Matrix(int nrows, int ncols) {
		this.nrows = nrows;
		this.ncols = ncols;
		this.values = new double[nrows][ncols];
	}

	public Matrix(double[][] values) {
		this.nrows = values.length;
		this.ncols = values[0].length;
		this.values = values;
	}

	public Matrix add(Matrix mat) {
		if (nrows != mat.nrows || ncols != mat.ncols) {
			return null;
		}

		double[][] newValues = new double[nrows][ncols];
		for (int i = 0; i < nrows; i++) {
			for (int j = 0; j < ncols; j++) {
				newValues[i][j] = values[i][j] + mat.values[i][j];
			}
		}

		return (new Matrix(newValues));
	}

        public Matrix substract(Matrix mat) {
		if (nrows != mat.nrows || ncols != mat.ncols) {
			return null;
		}

		double[][] newValues = new double[nrows][ncols];
		for (int i = 0; i < nrows; i++) {
			for (int j = 0; j < ncols; j++) {
				newValues[i][j] = values[i][j] - mat.values[i][j];
			}
		}

		return (new Matrix(newValues));
	}

	public Matrix multiplicate(Matrix mat) {
		if (ncols != mat.nrows) {
			return null;
		}

		double[][] newValues = new double[nrows][mat.ncols];
		for (int i = 0; i < nrows; i++) {
			for (int j = 0; j < mat.ncols; j++) {
				double sum = 0;
				for (int k = 0; k < ncols; k++) {
					sum += values[i][k] * mat.values[k][j];
				}
				newValues[i][j] = sum;
			}
		}

		return (new Matrix(newValues));
	}
	
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < nrows; i++) {
			for (int j = 0; j < ncols; j++) {
				sb.append("\t" + values[i][j]);
			}
			sb.append("\n");
		}

		return sb.toString();
	}
}