.. py:function:: laplacian(fs)
Computes the Laplacian of each field in ``fs``.
:param fs: input fieldset
:type fs: :class:`Fieldset`
:rtype: :class:`Fieldset`
The computations for a field f are based on the following formula:
.. math::
\triangle f =\frac{1}{R^2 \ cos^2\phi}\frac{\partial^2 f}{\partial \lambda^2} + \frac{1}{R^2}\frac{\partial^2 f}{\partial \phi^2} - \frac{1}{R^2}tan\phi\frac{\partial f}{\partial \phi}
where:
* R: radius of the Earth
* :math:`\phi`: latitude
* :math:`\lambda`: longitude.
The derivatives are computed with a second order finite-difference approximation. The resulting fields contain missing values on the poles.
.. warning::
:func:`laplacian` is only implemented for regular latitude-longitude grids.
.. mv-minigallery:: laplacian