docs: def lindblad_operator(A, rho):
      r"""This function returns the action of a Lindblad operator A on a density
      matrix rho. This is defined as :
          L(A,rho) = A*rho*A.adjoint()
                   - (A.adjoint()*A*rho + rho*A.adjoint()*A)/2.
  
      >>> rho=define_density_matrix(3)
      >>> lindblad_operator( ketbra(1,2,3) ,rho )
      Matrix([
      [   rho22, -rho12/2,        0],
      [-rho21/2,   -rho22, -rho23/2],
      [       0, -rho32/2,        0]])
  
      """
      return A*rho*A.adjoint() - (A.adjoint()*A*rho + rho*A.adjoint()*A)/2