code: def recommended_overlap(name, nfft=None):
      
      try:
          name = canonical_name(name)
      except KeyError as exc:
          raise ValueError(str(exc))
      try:
          rov = ROV[name]
      except KeyError:
          raise ValueError("no recommended overlap for %r window" % name)
      if nfft:
          return int(ceil(nfft * rov))
      return rov
docs: Returns the recommended fractional overlap for the given window
  
      If ``nfft`` is given, the return is in samples
  
      Parameters
      ----------
      name : `str`
          the name of the window you are using
  
      nfft : `int`, optional
          the length of the window
  
      Returns
      -------
      rov : `float`, `int`
          the recommended overlap (ROV) for the given window, in samples if
          ``nfft` is given (`int`), otherwise fractional (`float`)
  
      Examples
      --------
      >>> from gwpy.signal.window import recommended_overlap
      >>> recommended_overlap('hann')
      0.5
      >>> recommended_overlap('blackmanharris', nfft=128)
      85