code: def energy_minimum(self, x):
      
      E      = self.energy
      y_min  = self.find_energy_minimum(E, x)
      return y_min
docs: Given an input array `x` it returns its associated encoding `y(x)`, that is, 
      a stable configuration (local energy minimum) of the hidden units 
      while the visible units are clampled to `x`.