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Cauchy-Riemann and analytic nature It is necessary that the Cauchy/Riemann equations are satisfied for f(z) to be analytic in R
If the second partial derivatives of f exist and are continuous, these are sufficient as well.
Cauchy-Riemann equations (del u)/(del x) = (del v)/(del y)
(del u)/(del y) = -(del v)/(del x)
Complex potential SInce velocity potential phi is harmonic, there must exist a conjugate harmonic function psi(x,y) such that
Omega(z) = Phi(x,y) + i*Psi(x,y)
Complex velocity V = Vx + i*Vy = _(Omega’(z))
Conjugate coordinates x=(1/2)(z+z); y=(1/2i)(z-z)
Cross product z1 X z2 = x1y2 – x2y1 = Im(_z1*z2)
Definition of differentiation f’(z) = lim(dz->0) (f(z+dz)-f(z))/dz
DeMoivre’s Theorem zn = rn(cos ntheta + i sin n*theta)
Dirichlet Problem Let R be a simply-connected region bounded by asimple closed curve C.
Find a function phi which satisfies Laplace’s equation and takes prescribed values on the boundary C.
Dot product z1 dot z2 = x1×2 + y1y2 = Re(_z1*z2)
Electric field intensity E = -grad(Phi)
Equipotential line Phi(x,y) = alpha
Euler’s Equation ez = e(x+ iy) = e^x(cos theta + i sin theta)
Exponential function w = ez = e(x+iy)
Harmonic Functions 2nd partial of u/v exists wrt x/y and are continuous, then
(del2 u)(del x2) + (del2 u)(del y2) = 0
(del2 v)(del x2) + (del2 v)(del y2) = 0
Heat flux Q = -K((del Phi)/(del x) + i/(del y) = Qx + iQy
Isolated singular point z = z0 is isolated if we can find delta>0 such that |z-z0| = delta encloses no singular point but z_0
L’Hospital’s Rule If f(z) and g(z) are analytic containing z0, f(z0)=g(z0)=0, but g’(z0) != 0 then
lim(z->z0)f(z)/g(z) = f’(z0)/g’(z_0)
Laplace’s Equation Del2 phi = (del2 phi)/(del x2) + (del2 phi)/(del y^2)
Linear function w = az+b
Log function w = ln z = ln r + i(theta + 2k*pi), k = 0, +-1,...
Neumann Problem Let R be a simply-connected region bounded by a simple closed curve C.
Find a function phi which satisfies Laplace’s equation and whose normal derivative (del phi)/(del n) takes prescribed values on the boundary C
Parametric equation for a line (x – x1) = t; (y-y1) – t(y2-y1)
Pole n exists such that lim(z->z0)(z-z0)^n*f(z) = a != 0
z=z_0 is a pole of order n
Polynomial w = a0zn + a1z(n-1) + a2*z^(n-2) + ... + an
Rational algebraic function w=P(z)/Q(z) where P and Q are polynomials
Roots: if w^n = z, then w= w = r^(1/n) { cos((theta + 2kpi)/n) + i sin((theta + 2kpi)/n) }
Streamline Phi(x,y) = Beta
Taylor series about point a f(z) = f(a) + f’(a)(z-a) + (f’‘(a)/2!)(z-a)2 + ... + (f’n(a)/n!)(z-a)n + ...
Taylor series about pt a where a=0 is called MacLaurin series
Velocity Potential If Vx and Vy denote components of velocity of a fluid, there exists a function phi called the velocity potential such that
Vx = (del phi)/(del x),
V
y = (del phi)/(del y)