code: func (s *Sinc) HighPassCoefs() []float64 {
  	if s == nil {
  		return nil
  	}
  	if s._highPassCoefs != nil && len(s._highPassCoefs) > 0 {
  		return s._highPassCoefs
  	}
  
  	// we take the low pass coesf and invert them
  	size := s.Taps + 1
  	s._highPassCoefs = make([]float64, size)
  	lowPassCoefs := s.LowPassCoefs()
  	winData := s.Window(size)
  
  	for i := 0; i < (s.Taps / 2); i++ {
  		s._highPassCoefs[i] = -lowPassCoefs[i]
  		s._highPassCoefs[size-1-i] = s._highPassCoefs[i]
  	}
  	s._highPassCoefs[s.Taps/2] = (1 - 2*s.TransitionFreq()) * winData[s.Taps/2]
  	return s._highPassCoefs
  }
docs: // HighPassCoefs returns the coeficients to create a high pass filter