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Replace apparently retired UDUNITS documentation link. #5153

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Feb 9, 2023
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Replace apparently retired UDUNITS documentation link. #5153

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32 changes: 16 additions & 16 deletions docs/src/userguide/cube_maths.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -5,8 +5,8 @@ Cube Maths
==========


The section :doc:`navigating_a_cube` highlighted that
every cube has a data attribute;
The section :doc:`navigating_a_cube` highlighted that
every cube has a data attribute;
this attribute can then be manipulated directly::

cube.data -= 273.15
Expand Down Expand Up @@ -37,7 +37,7 @@ Let's load some air temperature which runs from 1860 to 2100::
filename = iris.sample_data_path('E1_north_america.nc')
air_temp = iris.load_cube(filename, 'air_temperature')

We can now get the first and last time slices using indexing
We can now get the first and last time slices using indexing
(see :ref:`cube_indexing` for a reminder)::

t_first = air_temp[0, :, :]
Expand All @@ -50,8 +50,8 @@ We can now get the first and last time slices using indexing
t_first = air_temp[0, :, :]
t_last = air_temp[-1, :, :]

And finally we can subtract the two.
The result is a cube of the same size as the original two time slices,
And finally we can subtract the two.
The result is a cube of the same size as the original two time slices,
but with the data representing their difference:

>>> print(t_last - t_first)
Expand All @@ -70,8 +70,8 @@ but with the data representing their difference:

.. note::

Notice that the coordinates "time" and "forecast_period" have been removed
from the resultant cube;
Notice that the coordinates "time" and "forecast_period" have been removed
from the resultant cube;
this is because these coordinates differed between the two input cubes.


Expand Down Expand Up @@ -174,15 +174,15 @@ broadcasting behaviour::
Combining Multiple Phenomena to Form a New One
----------------------------------------------

Combining cubes of potential-temperature and pressure we can calculate
Combining cubes of potential-temperature and pressure we can calculate
the associated temperature using the equation:

.. math::

T = \theta (\frac{p}{p_0}) ^ {(287.05 / 1005)}

Where :math:`p` is pressure, :math:`\theta` is potential temperature,
:math:`p_0` is the potential temperature reference pressure
Where :math:`p` is pressure, :math:`\theta` is potential temperature,
:math:`p_0` is the potential temperature reference pressure
and :math:`T` is temperature.

First, let's load pressure and potential temperature cubes::
Expand All @@ -191,7 +191,7 @@ First, let's load pressure and potential temperature cubes::
phenomenon_names = ['air_potential_temperature', 'air_pressure']
pot_temperature, pressure = iris.load_cubes(filename, phenomenon_names)

In order to calculate :math:`\frac{p}{p_0}` we can define a coordinate which
In order to calculate :math:`\frac{p}{p_0}` we can define a coordinate which
represents the standard reference pressure of 1000 hPa::

import iris.coords
Expand All @@ -205,7 +205,7 @@ the :meth:`iris.coords.Coord.convert_units` method::

p0.convert_units(pressure.units)

Now we can combine all of this information to calculate the air temperature
Now we can combine all of this information to calculate the air temperature
using the equation above::

temperature = pot_temperature * ( (pressure / p0) ** (287.05 / 1005) )
Expand All @@ -219,12 +219,12 @@ The result could now be plotted using the guidance provided in the

.. only:: html

A very similar example to this can be found in
A very similar example to this can be found in
:ref:`sphx_glr_generated_gallery_meteorology_plot_deriving_phenomena.py`.

.. only:: latex

A very similar example to this can be found in the examples section,
A very similar example to this can be found in the examples section,
with the title "Deriving Exner Pressure and Air Temperature".

.. _cube_maths_combining_units:
Expand All @@ -249,7 +249,7 @@ unit (if ``a`` had units ``'m2'`` then ``a ** 0.5`` would result in a cube
with units ``'m'``).

Iris inherits units from `cf_units <https://scitools.org.uk/cf-units/docs/latest/>`_
which in turn inherits from `UDUNITS <https://www.unidata.ucar.edu/software/udunits/udunits-current/udunits2.html>`_.
which in turn inherits from `UDUNITS <https://docs.unidata.ucar.edu/udunits/current/>`_.
As well as the units UDUNITS provides, cf units also provides the units
``'no-unit'`` and ``'unknown'``. A unit of ``'no-unit'`` means that the
associated data is not suitable for describing with a unit, cf units
Expand Down