# Complex Analysis in plain view

Many of the functions that arise naturally in mathematics and real world applications can be extended to and regarded as complex functions, meaning the input, as well as the output, can be complex numbers $x+iy$ , where $i={\sqrt {-1}}$ , in such a way that it is a more natural object to study. Complex analysis, which used to be known as function theory or theory of functions of a single complex variable, is a sub-field of analysis that studies such functions (more specifically, holomorphic functions) on the complex plane, or part (domain) or extension (Riemann surface) thereof. It notably has great importance in number theory, e.g. the Riemann zeta function (for the distribution of primes) and other $L$ -functions, modular forms, elliptic functions, etc.

The shortest path between two truths in the real domain passes through the complex domain. — Jacques Hadamard

In a certain sense, the essence of complex functions is captured by the principle of analytic continuation.

## Complex Functions

Complex Function Note

1. Exp and Log Function Note (H1.pdf)
2. Trig and TrigH Function Note (H1.pdf)
3. Inverse Trig and TrigH Functions Note (H1.pdf)

## Residue Integrals

### Residue Integrals Note

• Laurent Series with the Residue Theorem Note (H1.pdf)
• Laurent Series with Applications Note (H1.pdf)
• Laurent Series and the z-Transform Note (H1.pdf)
• Laurent Series as a Geometric Series Note (H1.pdf)

### Laurent Series and the z-Transform Example Note

#### Geometric Series Examples

• Double Pole Case
- Examples (A.pdf, B.pdf)
- Properties (A.pdf, B.pdf)