code: def solve(self, v):
          
          from numpy_sugar.linalg import ddot
  
          self._init_svd()
          L = kron(self.Lh, self.Lx)
          return L.T @ ddot(self.D, L @ v, left=True)
docs: Implements the product K⁻¹⋅v.
  
          Parameters
          ----------
          v : array_like
              Array to be multiplied.
  
          Returns
          -------
          x : ndarray
              Solution x to the equation K⋅x = y.