docs: def ckm_standard(t12, t13, t23, delta):
      r"""CKM matrix in the standard parametrization and standard phase
      convention.
  
      Parameters
      ----------
  
      - `t12`: CKM angle $\theta_{12}$ in radians
      - `t13`: CKM angle $\theta_{13}$ in radians
      - `t23`: CKM angle $\theta_{23}$ in radians
      - `delta`: CKM phase $\delta=\gamma$ in radians
      """
      c12 = cos(t12)
      c13 = cos(t13)
      c23 = cos(t23)
      s12 = sin(t12)
      s13 = sin(t13)
      s23 = sin(t23)
      return np.array([[c12*c13,
          c13*s12,
          s13/exp(1j*delta)],
          [-(c23*s12) - c12*exp(1j*delta)*s13*s23,
          c12*c23 - exp(1j*delta)*s12*s13*s23,
          c13*s23],
          [-(c12*c23*exp(1j*delta)*s13) + s12*s23,
          -(c23*exp(1j*delta)*s12*s13) - c12*s23,
          c13*c23]])