code: def crossings_nonzero_pos2neg(data):
      
      import numpy as np
  
      if isinstance(data, np.ndarray):
          pass
      elif isinstance(data, list):
          data = np.asarray(data)
      else:
          raise IOError('data should be a numpy array')
  
      pos = data > 0
  
      crossings = (pos[:-1] & ~pos[1:]).nonzero()[0]
  
      return crossings
docs: Find `indices of zero crossings from positive to negative values <http://stackoverflow.com/questions/3843017/efficiently-detect-sign-changes-in-python>`_.
  
          :param data: numpy array of floats
          :type data: numpy array of floats
          :return crossings: crossing indices to data
          :rtype crossings: numpy array of integers
  
          :Examples:
  
          >>> import numpy as np
          >>> from mhealthx.signals import crossings_nonzero_pos2neg
          >>> data = np.random.random(100)
          >>> crossings = crossings_nonzero_pos2neg(data)