public Matrix minus(Matrix B) {
		Matrix A = this;
		if (B.M != A.M || B.N != A.N)
			throw new RuntimeException("Illegal matrix dimensions.");
		Matrix C = new Matrix(M, N);
		for (int i = 0; i < M; i++)
			for (int j = 0; j < N; j++)
				C.data[i][j] = new DataNode(A.data[i][j].value() - B.data[i][j].value());
		return C;
	}