code: def _overlap(y,yr,psd):
      
      yyr  = _inner_product(y,yr,psd)
      yy   = _inner_product(y,y,psd)
      yryr = _inner_product(yr,yr,psd)
      olap = yyr/np.sqrt(yy*yryr)
      return olap
docs: returns the detector noise weighted inner product