Three-dimensional Scale Factors
The three dimensional scale factors are:
It is seen that The scale factors and are the same as in the two-dimensional case. The infinitesimal volume element is then
and the Laplacian is given by
Other differential operators such as and can be expressed in the coordinates by substituting the scale factors into the general formulae found in orthogonal coordinates.
Read more about this topic: Parabolic Coordinates
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![\nabla^2 \Phi = \frac{1}{\sigma^{2} + \tau^{2}}
\left[
\frac{1}{\sigma} \frac{\partial}{\partial \sigma}
\left( \sigma \frac{\partial \Phi}{\partial \sigma} \right) +
\frac{1}{\tau} \frac{\partial}{\partial \tau}
\left( \tau \frac{\partial \Phi}{\partial \tau} \right)\right] +
\frac{1}{\sigma^2\tau^2}\frac{\partial^2 \Phi}{\partial \varphi^2}](http://upload.wikimedia.org/math/6/4/5/645a734321923bbd5ee7ac8e099e7a92.png)