code: def value(self):
          
          C0 = self._C0.value()
          C1 = self._C1.value()
          return kron(C0, self._GG) + kron(C1, self._I)
docs: Covariance matrix K = C₀ ⊗ GGᵀ + C₁ ⊗ I.
  
          Returns
          -------
          K : ndarray
              C₀ ⊗ GGᵀ + C₁ ⊗ I.