code: public function multiply($z)
      {
          if (is_numeric($z)) {
              $z = new self($z, 0);
          }
  
          return new self(
              ($this->float_r * $z->re) - ($this->float_i * $z->im),
              ($this->float_r * $z->im) + ($z->re * $this->float_i)
          );
      }
docs: Multiplies current complex number with another.
  
  @param  mixed   $z Complex or real number
  @access public
  @return Complex