Cartesian 3D
============
Identical to the Cartesian 2D example except this time extend the computational
grid by 8 nodes in the z direction.

.. code-block:: python

   import numpy as np
   import pykonal

   # Initialize the solver.
   solver = pykonal.EikonalSolver(coord_sys="cartesian")
   solver.velocity.min_coords = 0, 0, 0
   solver.velocity.node_intervals = 1, 1, 1
   # This time we want a 3D computational grid, so set the number of grid nodes
   # in the z direction to 8 as well.
   solver.velocity.npts = 8, 8, 8
   solver.velocity.values = np.ones(solver.velocity.npts)

   # Initialize the source.
   src_idx = 0, 0, 0
   solver.traveltime.values[src_idx] = 0
   solver.unknown[src_idx] = False
   solver.trial.push(*src_idx)

   # Solve the system.
   solver.solve()

.. image:: figures/cartesian_3d.png