def comp_r_prec
      gamma = comp_gamma_p
      phi   = comp_phi_p
      psi   = comp_psi_p
      r = r_z(gamma)
      r = r_x(phi,   r)
      r = r_z(-psi,  r)
      r = r_x(-@eps, r)
      return r
    rescue => e
      raise
    end
def comp_r_prec
      gamma = comp_gamma_p
      phi   = comp_phi_p
      psi   = comp_psi_p
      r = r_z(gamma)
      r = r_x(phi,   r)
      r = r_z(-psi,  r)
      r = r_x(-@eps, r)
      return r
    rescue => e
      raise
    end
=========================================================================
 precession（歳差）変換行列（J2000.0 用）

 * 歳差の変換行列
     P(ε , ψ , φ , γ ) = R1(-ε ) * R3(-ψ ) * R1(φ ) * R3(γ )
   但し、R1, R2, R3 は x, y, z 軸の回転。
              + 1     0      0   +            +  cosθ   sinθ   0 +
     R1(θ ) = | 0   cosθ   sinθ  | , R3(θ ) = | -sinθ   cosθ   0 |
              + 0  -sinθ   cosθ  +            +    0      0    1 +
                     + P_11 P_12 P_13 +
     P(ε, ψ, φ, γ) = | P_21 P_22 P_23 | とすると、
                     + P_31 P_32 P_33 +
     P_11 = cosψ cosγ + sinψ cosφ sinγ
     P_12 = cosψ sinγ - sinψ cosφ ̄cosγ
     P_13 = -sinψ sinφ
     P_21 = cosε sinψ cosγ - (cosε cosψ cosφ + sinε sinφ )sinγ
     P_22 = cosε sinψ cosγ + (cosε cosψ cosφ + sinε sinφ )cosγ
     P_23 = cosε cosψ sinφ - sinε cosφ
     P_31 = sinε sinψ cosγ - (sinε cosψ cosφ - cosε sinφ)sinγ
     P_32 = sinε sinψ cosγ + (sinε cosψ cosφ - cosε sinφ)cosγ
     P_33 = sinε cosψ sinφ + cosε cosφ

 @param:  <none>
 @return: r  (変換行列)
=========================================================================