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In page-479 of Visual Complex Analysis, Tristan Needham derives the flux of a vector field in Geometric form:

$$ \nabla \cdot X = \partial_s |X| + \kappa_p |X|$$

The $\partial_s$ is a derivative along streamlines of the vector field $X$ an $\kappa_p$ is the curvature of the orthogonal streamline at the point we are taking divergence at.

Where did this formula originate from, and, what other sources discuss it? There is nothing of it on wikipedia. The book itself I couldn't find any reference to the formula in Modern literature, but is it still true in 2022 ?

In page-479 of Visual Complex Analysis, Tristan Needham derives the flux of a vector field in Geometric form:

$$ \nabla \cdot X = \partial_s |X| + \kappa_p |X|$$

The $\partial_s$ is a derivative along streamlines of the vector field $X$ an $\kappa_p$ is the curvature of the orthogonal streamline at the point we are taking divergence at.

Where did this formula originate from, and, what other sources discuss it? There is nothing of it on wikipedia. The book itself claims it couldn't find any reference to the formula in Modern literature, but is it still true in 2022 ?

In page-479 of Visual Complex Analysis, Tirstan Needham derives the flux of a vector field in Geometric form:

$$ \nabla \cdot X = \partial_s |X| + \kappa_p |X|$$

The $\partial_s$ is a derivative along streamlines of the vector field $X$ an $\kappa_S$ is the curvature of the orthogonal streamline at the point we are taking divergence at.

Where did this formula originate from, and, what other sources discuss it? There is nothing of it on wikipedia. The book itself it couldn't find any reference to the formula in Modern literature, but is it still true in 2022?

In page-479 of Visual Complex Analysis, Tristan Needham derives the flux of a vector field in Geometric form:

$$ \nabla \cdot X = \partial_s |X| + \kappa_p |X|$$

The $\partial_s$ is a derivative along streamlines of the vector field $X$ an $\kappa_p$ is the curvature of the orthogonal streamline at the point we are taking divergence at.

Where did this formula originate from, and, what other sources discuss it? There is nothing of it on wikipedia. The book itself I couldn't find any reference to the formula in Modern literature, but is it still true in 2022  ?

In page-479 of Visual Complex Analysis, Tirstan Needham derives the flux of a vector field in Geometric form:

$$ \nabla \cdot X = \partial_s |X| + \kappa_p |X|$$

The $\partial_s$ is a derivative along streamlines of the vector field $X$ and $\kappa_S$ is the curvature of the streamline at the point we are taking divergence at.

Where did this formula originate from, and, what other sources discuss it? There is nothing of it on wikipedia. The book itself it couldn't find any reference to the formula in Modern literature, but is it still true in 2022?

In page-479 of Visual Complex Analysis, Tirstan Needham derives the flux of a vector field in Geometric form:

$$ \nabla \cdot X = \partial_s |X| + \kappa_p |X|$$

The $\partial_s$ is a derivative along streamlines of the vector field $X$ an $\kappa_S$ is the curvature of the orthogonal streamline at the point we are taking divergence at.

Where did this formula originate from, and, what other sources discuss it? There is nothing of it on wikipedia. The book itself it couldn't find any reference to the formula in Modern literature, but is it still true in 2022?