LaTeX技巧207：使用align环境输入多行公式的技巧

align是输入多行公式中最好用的环境，仅仅是个人浅见，因为他的对齐非常灵活，如果大家需要非常灵巧的对齐方式的多行公式，建议使用align环境，对应的也还有align*和aligned等等类似的环境，这里不再详述。下文提供代码，尽展其风姿绰约。
演示效果图：



 


演示代码：
documentclass{article}
pagestyle{empty}
setcounter{page}{6}
setlength extwidth{266.0pt}
usepackage{CJK}
usepackage{amsmath}

egin{CJK}{GBK}{song}
egin{document}

egin{align}
  (a + b)^3  &= (a + b) (a + b)^2        \
             &= (a + b)(a^2 + 2ab + b^2) \
             &= a^3 + 3a^2b + 3ab^2 + b^3
end{align}
egin{align}
  x^2  + y^2 & = 1                       \
  x          & = sqrt{1-y^2}
end{align}
This example has two column-pairs.
egin{align}     ext{Compare }
  x^2 + y^2 &= 1               &
  x^3 + y^3 &= 1               \
  x         &= sqrt   {1-y^2} &
  x         &= sqrt[3]{1-y^3}
end{align}
This example has three column-pairs.
egin{align}
    x    &= y      & X  &= Y  &
      a  &= b+c               \
    x'   &= y'     & X' &= Y' &
      a' &= b                 \
  x + x' &= y + y'            &
  X + X' &= Y + Y' & a'b &= c'b
end{align}

This example has two column-pairs.
egin{flalign}   ext{Compare }
  x^2 + y^2 &= 1               &
  x^3 + y^3 &= 1               \
  x         &= sqrt   {1-y^2} &
  x         &= sqrt[3]{1-y^3}
end{flalign}
This example has three column-pairs.
egin{flalign}
    x    &= y      & X  &= Y  &
      a  &= b+c               \
    x'   &= y'     & X' &= Y' &
      a' &= b                 \
  x + x' &= y + y'            &
  X + X' &= Y + Y' & a'b &= c'b
end{flalign}

This example has two column-pairs.
enewcommandminalignsep{0pt}
egin{align}     ext{Compare }
  x^2 + y^2 &= 1               &
  x^3 + y^3 &= 1              \
  x         &= sqrt   {1-y^2} &
  x         &= sqrt[3]{1-y^3}
end{align}
This example has three column-pairs.
enewcommandminalignsep{15pt}
egin{flalign}
    x    &= y      & X  &= Y  &
      a  &= b+c              \
    x'   &= y'     & X' &= Y' &
      a' &= b                \
  x + x' &= y + y'            &
  X + X' &= Y + Y' & a'b &= c'b
end{flalign}

enewcommandminalignsep{2em}
egin{align}
  x      &= y      && ext{by hypothesis} \
      x' &= y'     && ext{by definition} \
  x + x' &= y + y' && ext{by Axiom 1}
end{align}

egin{equation}
egin{aligned}
  x^2 + y^2  &= 1               \
  x          &= sqrt{1-y^2}    \
  ext{and also }y &= sqrt{1-x^2}
end{aligned}               qquad
egin{gathered}
 (a + b)^2 = a^2 + 2ab + b^2    \
 (a + b) cdot (a - b) = a^2 - b^2
end{gathered}      end{equation}

egin{equation}
egin{aligned}[b]
  x^2 + y^2  &= 1               \
  x          &= sqrt{1-y^2}    \
  ext{and also }y &= sqrt{1-x^2}
end{aligned}               qquad
egin{gathered}[t]
 (a + b)^2 = a^2 + 2ab + b^2    \
 (a + b) cdot (a - b) = a^2 - b^2
end{gathered}
end{equation}
ewenvironment{rcase}
    {left.egin{aligned}}
    {end{aligned} ight brace}

egin{equation*}
  egin{rcase}
    B' &= -partial imes E          \
    E' &=  partial imes B - 4pi j \,
  end{rcase}
  quad ext {Maxwell's equations}
end{equation*}

egin{equation} egin{aligned}
  V_j &= v_j                      &
  X_i &= x_i - q_i x_j            &
      &= u_j + sum_{i e j} q_i \
  V_i &= v_i - q_i v_j            &
  X_j &= x_j                      &
  U_i &= u_i
end{aligned} end{equation}

egin{align}
  A_1 &= N_0 (lambda ; Omega')
         -  phi ( lambda ; Omega')   \
  A_2 &= phi (lambda ; Omega')
            phi (lambda ; Omega)     \
intertext{and finally}
  A_3 &= mathcal{N} (lambda ; omega)
end{align}
end{CJK}
end{document}

from: http://blog.sina.com.cn/s/blog_5e16f1770100gror.html