Definition:Cauchy-Riemann Equations

Definition
Let $D \subseteq \C$ be an open subset of the set of complex numbers $\C$.

Let $f: D \to \C$ be a complex function on $D$.

Let $u, v: \set {\tuple {x, y} \in \R^2: x + i y = z \in D} \to \R$ be the two real-valued functions defined as:

where:
 * $\map \Re {\map f z}$ denotes the real part of $\map f z$
 * $\map \Im {\map f z}$ denotes the imaginary part of $\map f z$.

The Cauchy-Riemann equations are the following equations:

which hold for the partial derivatives of $u$ and $v$ :


 * $f$ is complex-differentiable in $D$


 * $u$ and $v$ are differentiable in their entire domain.