   Open Disks are Open, Derivatives, Analyticity, Linear Approximations by
Video Lecture 10 of 35
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### Lecture Description

(0:00) Exam 1 in two class periods. (0:36) Modulus taking is operation preserving with respect to multiplication and division. (1:20) Proof that open disks are open sets. (13:23) Possible proofs on Exam 1. (14:29) Differentiability at a point. (17:16) Calculate the derivative of f(z) = z^3 from the limit definition. (24:21) Be able to derive basic derivative rules (linearity & product rule especially...look up the derivation of the product rule) using the field properties ("ordinary" algebraic properties) of C. (30:57) Even simple complex functions can fail to be differentiable (such as the function that returns the complex conjugate of a given number) which is an example you should study. (32:53) Definition of what it means for a complex function to be analytic at a point. (36:04) Analyticity of a function defined on an open set. (39:19) Polynomials are analytic everywhere on C (they are "entire") and rational functions are analytic everywhere that they are defined. (42:01) This is related to the Cauchy-Riemann equations. (42:34) Linear approximation for real differentiable planar mappings (equations, approximations, and animation of geometric meaning). (53:27) Linear approximation for complex differentiable mappings.

### Course Description

Based on "Fundamentals of Complex Analysis, with Applications to Engineering and Science", by E.B. Saff and A.D. Snider (3rd Edition). "Visual Complex Analysis", by Tristan Needham, is also referred to a lot. Mathematica is often used, especially to visualize complex analytic (conformal) mappings.