code: def find_peaks(signal):
      
      derivative = np.gradient(signal, 2)
      peaks = np.where(np.diff(np.sign(derivative)))[0]
      return(peaks)
docs: Locate peaks based on derivative.
  
      Parameters
      ----------
      signal : list or array
          Signal.
  
      Returns
      ----------
      peaks : array
          An array containing the peak indices.
  
      Example
      ----------
      >>> signal = np.sin(np.arange(0, np.pi*10, 0.05))
      >>> peaks = nk.find_peaks(signal)
      >>> nk.plot_events_in_signal(signal, peaks)
  
      Notes
      ----------
      *Authors*
  
      - `Dominique Makowski <https://dominiquemakowski.github.io/>`_
  
      *Dependencies*
  
      - scipy
      - pandas