prompt: You will be provided with a partial code base and an issue statement explaining a problem to resolve.
  <issue>
  Create classes to represent ionization state distributions
  My plan for this PR is to create classes to represent the ionization state distributions of one or more elements.  I am going to add in a bunch of dunder methods like `__getitem__` and maybe `__call__` to help making access to the ionization states more straightfoward and intuitive.  Any suggestions on the naming convention will be helpful so that we can maximize readability. 
  
  Eventually we'll need a way to calculate ionization state distributions assuming collisional ionization equilibrium, but that will be for a different PR.  The purpose of this PR is to set up how to store and access the ionization distributions.  This will be discussed in #352.
  
  This will address some of #352.  It will probably be best to wait until after the `0.1.0` release to merge this, since this PR is only for a partial implementation anyway.
  
  
  
  </issue>
  <code>
  [start of plasmapy/classes/sources/plasma3d.py]
  1 """
  2 Defines the core Plasma class used by PlasmaPy to represent plasma properties.
  3 """
  4 
  5 import numpy as np
  6 import astropy.units as u
  7 import itertools
  8 
  9 from plasmapy.formulary.magnetostatics import MagnetoStatics
  10 
  11 from astropy.constants import mu0
  12 
  13 from plasmapy.classes import GenericPlasma
  14 
  15 __all__ = [
  16     "Plasma3D"
  17 ]
  18 
  19 
  20 class Plasma3D(GenericPlasma):
  21     """
  22     Core class for describing and calculating plasma parameters with
  23     spatial dimensions.
  24 
  25     Attributes
  26     ----------
  27     x : `astropy.units.Quantity`
  28         x-coordinates within the plasma domain. Equal to the
  29         `domain_x` input parameter.
  30     y : `astropy.units.Quantity`
  31         y-coordinates within the plasma domain. Equal to the
  32         `domain_y` input parameter.
  33     z : `astropy.units.Quantity`
  34         z-coordinates within the plasma domain. Equal to the
  35         `domain_z` input parameter.
  36     grid : `astropy.units.Quantity`
  37         (3, x, y, z) array containing the values of each coordinate at
  38         every point in the domain.
  39     domain_shape : tuple
  40         Shape of the plasma domain.
  41     density : `astropy.units.Quantity`
  42         (x, y, z) array of mass density at every point in the domain.
  43     momentum : `astropy.units.Quantity`
  44         (3, x, y, z) array of the momentum vector at every point in
  45         the domain.
  46     pressure : `astropy.units.Quantity`
  47         (x, y, z) array of pressure at every point in the domain.
  48     magnetic_field : `astropy.units.Quantity`
  49         (3, x, y, z) array of the magnetic field vector at every point
  50         in the domain.
  51 
  52     Parameters
  53     ----------
  54     domain_x : `astropy.units.Quantity`
  55         1D array of x-coordinates for the plasma domain. Must have
  56         units convertable to length.
  57     domain_y : `astropy.units.Quantity`
  58         1D array of y-coordinates for the plasma domain. Must have
  59         units convertable to length.
  60     domain_z : `astropy.units.Quantity`
  61         1D array of z-coordinates for the plasma domain. Must have
  62         units convertable to length.
  63 
  64     """
  65     @u.quantity_input(domain_x=u.m, domain_y=u.m, domain_z=u.m)
  66     def __init__(self, domain_x, domain_y, domain_z):
  67         # Define domain sizes
  68         self.x = domain_x
  69         self.y = domain_y
  70         self.z = domain_z
  71 
  72         self.grid = np.array(np.meshgrid(self.x, self.y, self.z,
  73                                          indexing='ij'))
  74         self.domain_shape = (len(self.x), len(self.y), len(self.z))
  75 
  76         # Initiate core plasma variables
  77         self.density = np.zeros(self.domain_shape) * u.kg / u.m**3
  78         self.momentum = np.zeros((3, *self.domain_shape)) * u.kg / (u.m ** 2 * u.s)
  79         self.pressure = np.zeros(self.domain_shape) * u.Pa
  80         self.magnetic_field = np.zeros((3, *self.domain_shape)) * u.T
  81         self.electric_field = np.zeros((3, *self.domain_shape)) * u.V / u.m
  82 
  83     @property
  84     def velocity(self):
  85         return self.momentum / self.density
  86 
  87     @property
  88     def magnetic_field_strength(self):
  89         B = self.magnetic_field
  90         return np.sqrt(np.sum(B * B, axis=0))
  91 
  92     @property
  93     def electric_field_strength(self):
  94         E = self.electric_field
  95         return np.sqrt(np.sum(E * E, axis=0))
  96 
  97     @property
  98     def alfven_speed(self):
  99         B = self.magnetic_field
  100         rho = self.density
  101         return np.sqrt(np.sum(B * B, axis=0) / (mu0 * rho))
  102 
  103     @classmethod
  104     def is_datasource_for(cls, **kwargs):
  105         if len(kwargs) == 3:
  106             match = all(f'domain_{direction}' in kwargs.keys() for direction in 'xyz')
  107         else:
  108             match = False
  109         return match
  110 
  111     def add_magnetostatic(self, *mstats: MagnetoStatics):
  112         # for each MagnetoStatic argument
  113         for mstat in mstats:
  114             # loop over 3D-index (ix,iy,iz)
  115             for point_index in itertools.product(*[list(range(n)) for n in self.domain_shape]):
  116                 # get coordinate
  117                 p = self.grid[(slice(None),)+point_index]  # function as [:, *index]
  118                 # calculate magnetic field at this point and add back
  119                 self.magnetic_field[(slice(None),)+point_index] += mstat.magnetic_field(p)
  120
  [end of plasmapy/classes/sources/plasma3d.py]
  </code>
  
  I need you to solve this issue by generating a single patch file that I can apply directly to this repository using git apply. Please respond with a single patch file in the following format.
  <patch>
  diff --git a/file.py b/file.py
  --- a/file.py
  +++ b/file.py
  @@ -1,27 +1,35 @@
   def euclidean(a, b):
  -    while b:
  -        a, b = b, a % b
  -    return a
  +    if b == 0:
  +        return a
  +    return euclidean(b, a % b)
   
   
   def bresenham(x0, y0, x1, y1):
       points = []
       dx = abs(x1 - x0)
       dy = abs(y1 - y0)
  -    sx = 1 if x0 < x1 else -1
  -    sy = 1 if y0 < y1 else -1
  -    err = dx - dy
  +    x, y = x0, y0
  +    sx = -1 if x0 > x1 else 1
  +    sy = -1 if y0 > y1 else 1
   
  -    while True:
  -        points.append((x0, y0))
  -        if x0 == x1 and y0 == y1:
  -            break
  -        e2 = 2 * err
  -        if e2 > -dy:
  -            err -= dy
  -            x0 += sx
  -        if e2 < dx:
  -            err += dx
  -            y0 += sy
  +    if dx > dy:
  +        err = dx / 2.0
  +        while x != x1:
  +            points.append((x, y))
  +            err -= dy
  +            if err < 0:
  +                y += sy
  +                err += dx
  +            x += sx
  +    else:
  +        err = dy / 2.0
  +        while y != y1:
  +            points.append((x, y))
  +            err -= dx
  +            if err < 0:
  +                x += sx
  +                err += dy
  +            y += sy
  +
  +    points.append((x, y))
       return points
  
  </patch>
golden_diff: diff --git a/plasmapy/classes/sources/plasma3d.py b/plasmapy/classes/sources/plasma3d.py
  --- a/plasmapy/classes/sources/plasma3d.py
  +++ b/plasmapy/classes/sources/plasma3d.py
  @@ -110,9 +110,10 @@
   
       def add_magnetostatic(self, *mstats: MagnetoStatics):
           # for each MagnetoStatic argument
  +        prod = itertools.product(*[list(range(n)) for n in self.domain_shape])
           for mstat in mstats:
               # loop over 3D-index (ix,iy,iz)
  -            for point_index in itertools.product(*[list(range(n)) for n in self.domain_shape]):
  +            for point_index in prod:
                   # get coordinate
                   p = self.grid[(slice(None),)+point_index]  # function as [:, *index]
                   # calculate magnetic field at this point and add back
  
verification_info: {"golden_diff": "diff --git a/plasmapy/classes/sources/plasma3d.py b/plasmapy/classes/sources/plasma3d.py\n--- a/plasmapy/classes/sources/plasma3d.py\n+++ b/plasmapy/classes/sources/plasma3d.py\n@@ -110,9 +110,10 @@\n \n     def add_magnetostatic(self, *mstats: MagnetoStatics):\n         # for each MagnetoStatic argument\n+        prod = itertools.product(*[list(range(n)) for n in self.domain_shape])\n         for mstat in mstats:\n             # loop over 3D-index (ix,iy,iz)\n-            for point_index in itertools.product(*[list(range(n)) for n in self.domain_shape]):\n+            for point_index in prod:\n                 # get coordinate\n                 p = self.grid[(slice(None),)+point_index]  # function as [:, *index]\n                 # calculate magnetic field at this point and add back\n", "issue": "Create classes to represent ionization state distributions\nMy plan for this PR is to create classes to represent the ionization state distributions of one or more elements.  I am going to add in a bunch of dunder methods like `__getitem__` and maybe `__call__` to help making access to the ionization states more straightfoward and intuitive.  Any suggestions on the naming convention will be helpful so that we can maximize readability. \r\n\r\nEventually we'll need a way to calculate ionization state distributions assuming collisional ionization equilibrium, but that will be for a different PR.  The purpose of this PR is to set up how to store and access the ionization distributions.  This will be discussed in #352.\r\n\r\nThis will address some of #352.  It will probably be best to wait until after the `0.1.0` release to merge this, since this PR is only for a partial implementation anyway.\r\n\r\n\n", "before_files": [{"content": "\"\"\"\nDefines the core Plasma class used by PlasmaPy to represent plasma properties.\n\"\"\"\n\nimport numpy as np\nimport astropy.units as u\nimport itertools\n\nfrom plasmapy.formulary.magnetostatics import MagnetoStatics\n\nfrom astropy.constants import mu0\n\nfrom plasmapy.classes import GenericPlasma\n\n__all__ = [\n    \"Plasma3D\"\n]\n\n\nclass Plasma3D(GenericPlasma):\n    \"\"\"\n    Core class for describing and calculating plasma parameters with\n    spatial dimensions.\n\n    Attributes\n    ----------\n    x : `astropy.units.Quantity`\n        x-coordinates within the plasma domain. Equal to the\n        `domain_x` input parameter.\n    y : `astropy.units.Quantity`\n        y-coordinates within the plasma domain. Equal to the\n        `domain_y` input parameter.\n    z : `astropy.units.Quantity`\n        z-coordinates within the plasma domain. Equal to the\n        `domain_z` input parameter.\n    grid : `astropy.units.Quantity`\n        (3, x, y, z) array containing the values of each coordinate at\n        every point in the domain.\n    domain_shape : tuple\n        Shape of the plasma domain.\n    density : `astropy.units.Quantity`\n        (x, y, z) array of mass density at every point in the domain.\n    momentum : `astropy.units.Quantity`\n        (3, x, y, z) array of the momentum vector at every point in\n        the domain.\n    pressure : `astropy.units.Quantity`\n        (x, y, z) array of pressure at every point in the domain.\n    magnetic_field : `astropy.units.Quantity`\n        (3, x, y, z) array of the magnetic field vector at every point\n        in the domain.\n\n    Parameters\n    ----------\n    domain_x : `astropy.units.Quantity`\n        1D array of x-coordinates for the plasma domain. Must have\n        units convertable to length.\n    domain_y : `astropy.units.Quantity`\n        1D array of y-coordinates for the plasma domain. Must have\n        units convertable to length.\n    domain_z : `astropy.units.Quantity`\n        1D array of z-coordinates for the plasma domain. Must have\n        units convertable to length.\n\n    \"\"\"\n    @u.quantity_input(domain_x=u.m, domain_y=u.m, domain_z=u.m)\n    def __init__(self, domain_x, domain_y, domain_z):\n        # Define domain sizes\n        self.x = domain_x\n        self.y = domain_y\n        self.z = domain_z\n\n        self.grid = np.array(np.meshgrid(self.x, self.y, self.z,\n                                         indexing='ij'))\n        self.domain_shape = (len(self.x), len(self.y), len(self.z))\n\n        # Initiate core plasma variables\n        self.density = np.zeros(self.domain_shape) * u.kg / u.m**3\n        self.momentum = np.zeros((3, *self.domain_shape)) * u.kg / (u.m ** 2 * u.s)\n        self.pressure = np.zeros(self.domain_shape) * u.Pa\n        self.magnetic_field = np.zeros((3, *self.domain_shape)) * u.T\n        self.electric_field = np.zeros((3, *self.domain_shape)) * u.V / u.m\n\n    @property\n    def velocity(self):\n        return self.momentum / self.density\n\n    @property\n    def magnetic_field_strength(self):\n        B = self.magnetic_field\n        return np.sqrt(np.sum(B * B, axis=0))\n\n    @property\n    def electric_field_strength(self):\n        E = self.electric_field\n        return np.sqrt(np.sum(E * E, axis=0))\n\n    @property\n    def alfven_speed(self):\n        B = self.magnetic_field\n        rho = self.density\n        return np.sqrt(np.sum(B * B, axis=0) / (mu0 * rho))\n\n    @classmethod\n    def is_datasource_for(cls, **kwargs):\n        if len(kwargs) == 3:\n            match = all(f'domain_{direction}' in kwargs.keys() for direction in 'xyz')\n        else:\n            match = False\n        return match\n\n    def add_magnetostatic(self, *mstats: MagnetoStatics):\n        # for each MagnetoStatic argument\n        for mstat in mstats:\n            # loop over 3D-index (ix,iy,iz)\n            for point_index in itertools.product(*[list(range(n)) for n in self.domain_shape]):\n                # get coordinate\n                p = self.grid[(slice(None),)+point_index]  # function as [:, *index]\n                # calculate magnetic field at this point and add back\n                self.magnetic_field[(slice(None),)+point_index] += mstat.magnetic_field(p)\n", "path": "plasmapy/classes/sources/plasma3d.py"}]}