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Questions and Answers

Complex number $z=x+yi$ 的实部和虚部分别是?

  • Re(z) = yi, Im(z) = x
  • Re(z) = y, Im(z) = x
  • Re(z) = x, Im(z) = y (correct)
  • Re(z) = yi, Im(z) = yi
  • 如果函数 $f(z)$ 在点 $z_0$ 是解析的,那么它在 $z_0$ 的邻域内也是解析的?

  • 不一定
  • 正确 (correct)
  • 需要更多信息
  • 错误
  • 柯西-黎曼方程的正确形式是什么?

  • ∂u/∂x = ∂v/∂y, ∂u/∂y = -∂v/∂x (correct)
  • ∂u/∂x = ∂v/∂y, ∂u/∂y = ∂v/∂x
  • ∂u/∂x = ∂v/∂x, ∂u/∂y = ∂v/∂y
  • ∂u/∂x = -∂v/∂y, ∂u/∂y = ∂v/∂x
  • 柯西积分公式的正确形式是什么?

    <p>f(z_0) = (1/2πi) ∫_C f(z)/(z-z_0) dz</p> Signup and view all the answers

    如果函数 $f(z)$ 在点 $z_0$ 是极点,那么 $Res(f, z_0)$ 是什么?

    <p>有限值</p> Signup and view all the answers

    什么是复平面中的闭合曲线?

    <p>(piecewise-smooth) 曲线</p> Signup and view all the answers

    Study Notes

    Complex Analysis

    Complex Numbers

    • A complex number is a number of the form z = x + yi, where x and y are real numbers and i is the imaginary unit, satisfying i^2 = -1.
    • The set of complex numbers is denoted by .
    • The real and imaginary parts of a complex number z are denoted by Re(z) and Im(z), respectively.

    Functions of Complex Numbers

    • A function f(z) of a complex variable z is a function that maps each complex number z to a complex number w.
    • The function f(z) is said to be analytic at a point z_0 if it is differentiable at z_0 and in a neighborhood of z_0.
    • Cauchy-Riemann Equations: A function f(z) = u(x, y) + iv(x, y) is analytic at z_0 if and only if it satisfies the Cauchy-Riemann equations:
      • ∂u/∂x = ∂v/∂y
      • ∂u/∂y = -∂v/∂x

    Contour Integration

    • A contour is a piecewise-smooth curve in the complex plane.
    • The contour integral of a function f(z) over a contour C is denoted by ∫_C f(z) dz.
    • Cauchy's Integral Formula: If f(z) is analytic inside and on a contour C, and z_0 is a point inside C, then:
      • f(z_0) = (1/2πi) ∫_C f(z)/(z-z_0) dz

    Residue Theory

    • The residue of a function f(z) at a point z_0 is denoted by Res(f, z_0).
    • The residue theorem: If f(z) is analytic inside and on a contour C, except at a point z_0 inside C, then:
      • ∫_C f(z) dz = 2πi Res(f, z_0)
    • The residue of a function f(z) at a pole of order n can be calculated using:
      • Res(f, z_0) = (1/(n-1)!) lim_(z→z_0) (d^(n-1)/dz^(n-1))((z-z_0)^n f(z))

    Applications of Complex Analysis

    • Complex analysis has applications in:
      • Electrical engineering (e.g., circuit analysis)
      • Signal processing (e.g., Fourier transform)
      • Quantum mechanics (e.g., wave functions)
      • Number theory (e.g., prime number theorem)

    复分析

    复数

    • 复数是形如 z = x + yi 的数,其中 xy 是实数,i 是虚单位,满足 i^2 = -1
    • 复数的集合记为
    • 复数 z 的实部和虚部分别记为 Re(z)Im(z)

    复变函数

    • 复变函数 f(z) 是将每个复数 z 映射到另一个复数 w 的函数。
    • 函数 f(z) 在点 z_0 是可微分的当且仅当它在 z_0z_0 的邻域内是可微分的。
    • 柯西-黎曼方程:函数 f(z) = u(x, y) + iv(x, y)z_0 是可微分的当且仅当它满足柯西-黎曼方程:
      • ∂u/∂x = ∂v/∂y
      • ∂u/∂y = -∂v/∂x

    积分 along a contour

    • 剖面是复平面中的 piecewise-smooth 曲线。
    • 函数 f(z) 沿着剖面 C 的积分记为 ∫_C f(z) dz
    • 柯西积分公式:如果 f(z) 在剖面 C 内部和边界上是可微分的,并且 z_0C 内部的一点,那么:
      • f(z_0) = (1/2πi) ∫_C f(z)/(z-z_0) dz

    残余理论

    • 函数 f(z) 在点 z_0 的残余记为 Res(f, z_0)
    • 残余定理:如果 f(z) 在剖面 C 内部和边界上是可微分的,除了点 z_0 内部,那么:
      • ∫_C f(z) dz = 2πi Res(f, z_0)
    • 如果函数 f(z) 在点 z_0 有阶数为 n 的极点,那么可以使用以下公式计算残余:
      • Res(f, z_0) = (1/(n-1)!) lim_(z→z_0) (d^(n-1)/dz^(n-1))((z-z_0)^n f(z))

    复分析应用

    • 复分析在以下领域有应用:
      • 电气工程(例如,电路分析)
      • 信号处理(例如,傅里叶变换)
      • 量子力学(例如,波函数)
      • 数论(例如,素数定理)

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