The following series of posts comprises our introduction to complex analysis as taught by Professor Rowan Killip at the University of California, Los Angeles, during the Fall quarter of 2009. Where necessary, course notes have been supplemented with details written by the authors of this website using assistance from Complex Analysis by Elias Stein and Rami Shakarchi. The basic properties of complex numbers will be assumed allowing us to begin with the definition of a holomorphic (or complex-differentiable) function, the central notion in our study of complex analysis.

The basic properties of complex numbers will be assumed, allowing us to begin with the definition of a holomorphic (or complex-differentiable) function, the central notion in our study of complex analysis.

**Definition 1.1** *Suppose is an open set and . We say is holomorphic (or complex-differentiable) at if there exists We say is holomorphic on if it has this property for all .*

We can rewrite this formula in terms of the real and imaginary parts of to surmise the relationship between complex differentiability and real analytic differentiability. Let with and , and write where . Then,

We first notice that this is stronger than the differentiability of the real map in . In the real, multivariable case, the derivative of this map is a linear operator, namely, the Jacobian, ; in our equation above, the matrix on the right hand side is . Clearly, it is endowed with a distinct structure summarized in the following proposition.

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