public Matrix multiply(Matrix B){
        if (B.getN() != this.getM())
            return null;

        Matrix C = new Matrix(this.getN(), B.getM());
        int i=0,j=0;
        for(i=0; i<this.getN();i++)
            for(j=0; j<this.getM(); j++)
                C.setij(i,j, this.getH(i).multiple(B.getV(j)));
        return C;
    }