.. _example_13:

(13) Plotting of vector fields
------------------------------

In many areas, such as fluid dynamics and elasticity, it is desirable to
plot vector fields of various kinds. GMT provides a way to illustrate
2-component vector fields using the
:doc:`grdvector </grdvector>` utility. The two
components of the field (Cartesian or polar components) are stored in
separate grid files. In this example we use
:doc:`grdmath </grdmath>` to generate a surface
:math:`z(x, y) = x \cdot \exp(-x^2 -y^2)` and to calculate
:math:`\nabla z` by returning the *x*- and *y*-derivatives separately.
We superpose the gradient vector field and the surface *z* and also plot
the components of the gradient in separate windows. A
:doc:`pstext </pstext>` call to place a header finishes the plot

.. literalinclude:: /_verbatim/example_13.txt
   :language: bash

.. figure:: /_images/example_13.*
   :width: 500 px
   :align: center

   Display of vector fields in GMT.