code: def vrel(v1, v2):
      
      v1 = stypes.toDoubleVector(v1)
      v2 = stypes.toDoubleVector(v2)
      return libspice.vrel_c(v1, v2)
docs: Return the relative difference between two 3-dimensional vectors.
  
      http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/vrel_c.html
  
      :param v1: First vector 
      :type v1: 3-Element Array of floats
      :param v2: Second vector 
      :type v2: 3-Element Array of floats
      :return: the relative difference between v1 and v2.
      :rtype: float