// This software is a computer program whose purpose is to compute the FMM.
//
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@@ -26,26 +26,40 @@
*
* @brief Spherical coordinate system
*
* The spherical coordinate system (r radius, theta inclination, phi azimuth) is the following <br>
* x = r sin(theta) cos(phi) <br>
* y = r sin(theta) sin(phi) <br>
* z = r cos(theta) <br>
* We consider the spherical coordinate system \f$(r, \theta, \varphi)\f$ commonly used in physics. r is the radial distance, \f$\theta\f$ the polar/inclination angle and \f$\varphi\f$ the azimuthal angle.<br>
* The <b>radial distance</b> is the Euclidean distance from the origin O to P.<br>
* The <b>inclination (or polar angle) </b>is the angle between the zenith direction and the line segment OP.<br>
* The <b>azimuth (or azimuthal angle)</b> is the signed angle measured from the azimuth reference direction to the orthogonal projection of the line segment OP on the reference plane.<br>
*
* The spherical coordinates of a point can be obtained from its Cartesian coordinates (x, y, z) by the formulae
* \f$ \displaystyle r = \sqrt{x^2 + y^2 + z^2}\f$<br>