# Layers¶

Landlab has the ability to add layers to the grid. Two types of layers are currently supported. First is EventLayers in which each event is preserved as an entry into the datastructure, even if no deposition occurs. If you are interested in chronostratigraphy, this is probably what you are interested in. Second is MaterialLayers, in which each layer must contain some material. If an entire layer is eroded in MaterialLayers, the layer is removed. MaterialLayers will likely use less memory than EventLayers.

## Module contents¶

class EventLayers(number_of_stacks, allocated=0)[source]

Bases: object

Track EventLayers where each event is its own layer.

EventLayers are meant to represent a layered object in which each layer represents a event. Thus they are likely the most appropriate tool to use if the user is interested in chronostratigraphy. If erosion occurs, a new layer with zero thickness is created. Thus, EventLayers may not be the most memory efficent layers datastructure.

EventLayers exists in contrast to the MaterialLayers object which does not make a new layer if only erosion occurs and if the attributes of the new layer are equivalent to the attributes of the material at the surface of the layer stack.

allocated
dz
thickness
number_of_layers
number_of_stacks
surface_index
z
add()[source]
get_surface_values()[source]
Parameters: number_of_stacks (int) – Number of layer stacks to track.

Examples

>>> from landlab.layers.eventlayers import EventLayers


Create an empty layer stack with 5 stacks.

>>> layers = EventLayers(5)
>>> layers.number_of_stacks
5
>>> layers.number_of_layers
0


Add a layer with a uniform thickness.

>>> layers.add(1.5)
>>> layers.number_of_layers
1
>>> layers.dz
array([[ 1.5,  1.5,  1.5,  1.5,  1.5]])


Add a second layer with uneven thickness.

>>> layers.add([1., 2., .5, 5., 0.])
>>> layers.dz
array([[ 1.5,  1.5,  1.5,  1.5,  1.5],
[ 1. ,  2. ,  0.5,  5. ,  0. ]])


Adding a layer with negative thickness will remove existing layers for the top of the stack. Note that this will create a new layer with thickness zero that represents this ‘event’. If instead your application would prefer that no new row is added to the layers datastructure, you may want to consider the MaterialLayers object.

>>> layers.add(-1)
>>> layers.dz
array([[ 1.5,  1.5,  1. ,  1.5,  0.5],
[ 0. ,  1. ,  0. ,  4. ,  0. ],
[ 0. ,  0. ,  0. ,  0. ,  0. ]])


Get the index value of the layer within each stack at the topographic surface.

>>> layers.surface_index
array([0, 1, 0, 1, 0])

add(dz, **kwds)[source]

Add a layer to the stacks.

Parameters: dz (float or array_like) – Thickness to add to each stack.

Examples

>>> from landlab.layers.eventlayers import EventLayers


Create an empty layer stack with 3 stacks.

>>> layers = EventLayers(3)
>>> layers.number_of_layers
0


To add a layer of uniform thickness to every stack.

>>> layers.add(1.5)
>>> layers.number_of_layers
1
>>> layers.dz
array([[ 1.5,  1.5,  1.5]])


Add a second layer with uneven thickness.

>>> layers.add([1., 2., .5])
>>> layers.dz
array([[ 1.5,  1.5,  1.5],
[ 1. ,  2. ,  0.5]])


Adding a layer with negative thickness will remove existing layers for the top of the stack.

>>> layers.add(-1)
>>> layers.dz
array([[ 1.5,  1.5,  1. ],
[ 0. ,  1. ,  0. ],
[ 0. ,  0. ,  0. ]])


Use keywords to track properties of each layer. For instance, here we create a new stack and add a layer with a particular age. You can access the layer properties as if the object were a dictionary.

>>> layers = EventLayers(3)
>>> layers.dz
array([[ 1.,  1.,  1.]])
>>> layers['age']
array([[ 3.,  3.,  3.]])
>>> layers['age']
array([[ 3.,  3.,  3.],
[ 6.,  6.,  6.]])


Attributes for each layer will exist even if the the layer is associated with erosion.

>>> layers.add([-2, -1, 1], age=8.)
>>> layers.dz
array([[ 1.,  1.,  1.],
[ 0.,  1.,  2.],
[ 0.,  0.,  1.]])
>>> layers['age']
array([[ 3.,  3.,  3.],
[ 6.,  6.,  6.],
[ 8.,  8.,  8.]])


To get the values at the surface of the layer stack:

>>> layers.get_surface_values('age')
array([ 3.,  6.,  8.])

allocated

Total number of allocated layers.

Examples

>>> from landlab.layers.eventlayers import EventLayers

>>> layers = EventLayers(3)
>>> layers.number_of_layers
0
>>> layers.allocated == 0
True

>>> layers.add(15.)
>>> layers.number_of_layers
1
>>> layers.allocated == 7
True
>>> for _ in range(layers.allocated): layers.add(0.)
>>> layers.number_of_layers
8
>>> layers.allocated == 15
True


If you know how many layers you will ultimately have, you can allocated enough memory for them when you create your layer stacks.

>>> layers = EventLayers(3, allocated=15)
>>> layers.number_of_layers
0
>>> layers.allocated == 15
True

>>> layers.add(15.)
>>> layers.number_of_layers
1
>>> layers.allocated == 15
True
>>> for _ in range(layers.allocated): layers.add(0.)
>>> layers.number_of_layers
16
>>> layers.allocated == 24
True

dz

Thickness of each layer.

The thickness of each layer at each stack as an array of shape (number_of_layers, number_of_stacks).

Examples

>>> from landlab.layers.eventlayers import EventLayers


Initially there are no layers so there are not thicknesses.

>>> layers = EventLayers(3)
>>> layers.dz.shape == (0, 3)
True


Now add two layers, the first of uniform thickness and the second non-uniform and with some erosion.

>>> layers.add(15.)
>>> layers.add([1., -1., 2.])
>>> layers.dz
array([[ 15.,  14.,  15.],
[  1.,   0.,   2.]])

get_surface_values(name)[source]

Values of a field on the surface layer.

number_of_layers

Total number of layers.

Examples

>>> from landlab.layers.eventlayers import EventLayers

>>> layers = EventLayers(3)
>>> layers.number_of_layers
0

>>> layers.add(15.)
>>> layers.add([1., -1., 2.])
>>> layers.number_of_layers
2

number_of_stacks

Number of stacks.

reduce([start, ]stop[, step])[source]

Combine layers.

Reduce adjacent layers into a single layer.

Examples

>>> from landlab.layers.eventlayers import EventLayers


Create an empty layer stack with 3 stacks.

>>> layers = EventLayers(3)
>>> layers.number_of_layers
0


To add a layer of uniform thickness to every stack.

>>> layers.add(1.5)
>>> layers.number_of_layers
1
>>> layers.dz
array([[ 1.5,  1.5,  1.5]])


Add a second layer with uneven thickness.

>>> layers.add([1., 2., .5])
>>> layers.dz
array([[ 1.5,  1.5,  1.5],
[ 1. ,  2. ,  0.5]])


Combine all of the layers into a single layer.

>>> layers.reduce()
>>> layers.dz
array([[ 2.5,  3.5,  2. ]])


Add two additional layers to the top. The bottom-most layer is row 0, and the two new layers are rows 1 and 2.

>>> layers.add([1., 2., .5])
>>> layers.add([1., 2., .5])
>>> layers.dz
array([[ 2.5,  3.5,  2. ],
[ 1. ,  2. ,  0.5],
[ 1. ,  2. ,  0.5]])


Combine the two new layers (layers 1 and 2) into a single layer.

>>> layers.reduce(1, 3)
>>> layers.dz
array([[ 2.5,  3.5,  2. ],
[ 2. ,  4. ,  1. ]])

>>> layers.add([1., 2., .5])
>>> layers.add([1., 2., .5])
>>> layers.dz
array([[ 2.5,  3.5,  2. ],
[ 2. ,  4. ,  1. ],
[ 1. ,  2. ,  0.5],
[ 1. ,  2. ,  0.5]])


Combine the middle two layers.

>>> layers.reduce(1, 3)
>>> layers.dz
array([[ 2.5,  3.5,  2. ],
[ 3. ,  6. ,  1.5],
[ 1. ,  2. ,  0.5]])
>>> layers.add([1., 1., 1.])
>>> layers.dz
array([[ 2.5,  3.5,  2. ],
[ 3. ,  6. ,  1.5],
[ 1. ,  2. ,  0.5],
[ 1. ,  1. ,  1. ]])


Combine every two layers (layers 0 and 1 and combined, and layers 1 and 2 are combined).

>>> layers.reduce(0, 4, 2)
>>> layers.dz
array([[ 5.5,  9.5,  3.5],
[ 2. ,  3. ,  1.5]])


When layers are combined, thicknesses are summed but layer attributes can be combined in other ways (e.g. max, or mean)

>>> layers = EventLayers(3)
>>> layers.add([1, 1, 1], age=0.)
>>> layers.add([1, 2, 5], age=1.)
>>> layers.add([2, 2, 2], age=2.)
>>> layers.reduce(age=np.max)
>>> layers["age"]
array([[ 2.,  2.,  2.]])

>>> layers.add([2, 2, 2], age=3.)
>>> layers.add([2, 2, 2], age=4.)
>>> layers.reduce(1, 3, age=np.mean)
>>> layers["age"]
array([[ 2. ,  2. ,  2. ],
[ 3.5,  3.5,  3.5]])

surface_index

Index to the top non-empty layer.

Examples

>>> from landlab.layers.eventlayers import EventLayers


Create an empty layer stack with 5 stacks.

>>> layers = EventLayers(3)
>>> layers.surface_index
array([0, 0, 0])


Add a layer with a uniform thickness.

>>> for _ in range(5): layers.add(1.0)
>>> layers.surface_index
array([4, 4, 4])


Add a layer with varying thickness. Negative thickness removes thickness from underlying layers, zero thickness adds a layer but doesn’t change the surface index.

>>> layers.add([-1.0, 0.0, 1.0])
>>> layers.surface_index
array([3, 4, 5])

thickness

Total thickness of the columns.

The sum of all layer thicknesses for each stack as an array of shape (number_of_stacks, ).

Examples

>>> from landlab.layers.eventlayers import EventLayers


Initially there are no layers so the total thickness is 0.

>>> layers = EventLayers(3)
>>> layers.thickness
array([ 0.,  0.,  0.])


After adding some layers, the stacks have varying thicknesses.

>>> layers.add(15.)
>>> layers.add([1., -1., 2.])
>>> layers.thickness
array([ 16.,  14.,  17.])

tracking

Layer properties being tracked.

Examples

>>> from landlab.layers.eventlayers import EventLayers
>>> layers = EventLayers(3)
>>> layers.tracking
[]
>>> layers.tracking
['age']

z

Thickness to top of each layer.

Thickness from the bottom of each stack to the top of each layer as an array of shape (number_of_layers, number_of_stacks).

Examples

>>> from landlab.layers.eventlayers import EventLayers


Initially there are no layers so the elevation to the top is 0.

>>> layers = EventLayers(3)
>>> layers.z.shape == (0, 3)
True


After adding some layers, elevations are to the top of each layer.

>>> layers.add(15.)
>>> layers.add([1., -1., 2.])
>>> layers.dz
array([[ 15.,  14.,  15.],
[  1.,   0.,   2.]])
>>> layers.z
array([[ 15.,  14.,  15.],
[ 16.,  14.,  17.]])

class EventLayersMixIn[source]

Bases: object

MixIn that adds a EventLayers attribute to a ModelGrid.

at_layer

EventLayers for each cell.

event_layers

EventLayers for each cell.

class MaterialLayers(number_of_stacks, allocated=0)[source]

Track MaterialLayers where each layer has some material in it.

MaterialLayers are meant to represent a layered object in which each layer has some material in it. If erosion occurs, no new layer is created. These layers stand in contrast to the EventLayers for which each event is represented by a layer.

MaterialLayers is likely a more memory efficent data structure than EventLayers as it does not record erosion as an array of zeros.

Parameters: number_of_stacks (int) – Number of layer stacks to track.
allocated
dz
thickness
number_of_layers
number_of_stacks
surface_index
z
add()[source]
get_surface_values()

Examples

>>> from landlab.layers.materiallayers import MaterialLayers


Create an empty layer stack with 5 stacks.

>>> layers = MaterialLayers(5)
>>> layers.number_of_stacks
5
>>> layers.number_of_layers
0


Add a layer with a uniform thickness.

>>> layers.add(1.5)
>>> layers.number_of_layers
1
>>> layers.dz
array([[ 1.5,  1.5,  1.5,  1.5,  1.5]])


MaterialLayers will combine layers if they have the same attributes. Adding a second layer with uneven thickness. Will increment the first layers thickness. This stands in contrast with EventLayers which will track each addition as a separate entry in the layers datastructure.

>>> layers.add([1., 2., 3., 5., 0.])
>>> layers.dz
array([[ 2.5,  3.5,  4.5,  6.5,  1.5]])


Adding a layer with negative thickness will remove material from the layers. Unlike EventLayers, it will not add a layer of zeros that represent an event with no deposition.

>>> layers.add(-1)
>>> layers.dz
array([[ 1.5,  2.5,  3.5,  5.5,  0.5]])


Get the index value of the layer within each stack at the topographic surface.

>>> layers.surface_index
array([0, 0, 0, 0, 0])


See the example in the add method to learn how MaterialLayers behaves if material properties are also tracked.

add(dz, **kwds)[source]

Add a layer to the MaterialLayers stacks.

Parameters: dz (float or array_like) – Thickness to add to each stack.

Examples

>>> from landlab.layers.materiallayers import MaterialLayers


Create an empty layer stack with 3 stacks.

>>> layers = MaterialLayers(3)
>>> layers.number_of_layers
0


To add a layer of uniform thickness to every stack.

>>> layers.add(1.5)
>>> layers.number_of_layers
1
>>> layers.dz
array([[ 1.5,  1.5,  1.5]])


Add a second layer with uneven thickness.

>>> layers.add([1., 2., .5])
>>> layers.dz
array([[ 2.5,  3.5,  2. ]])


Because the attributes of this layer and the previous layer are the same (e.g. they don’t exist), MaterialLayer will combined them. This is the primary difference between MaterialLayers and EventLayers.

Adding a layer with negative thickness will remove material from the top of the stack.

>>> layers.add(-1)
>>> layers.dz
array([[ 1.5,  2.5,  1. ]])
>>> layers.number_of_layers
1


Use keywords to track properties of each layer. For instance, here we create a new stack and add a layer with a particular type and a particular size. You can access the layer properties as if the object were a dictionary.

>>> layers = MaterialLayers(3)
>>> layers.add(1., type=3., size='sand')
>>> layers.dz
array([[ 1.,  1.,  1.]])
>>> layers['type']
array([[ 3.,  3.,  3.]])


As you can see, there is no rule that says you can’t use a string as the value of an attribute.

Adding a layer with the same attributes as the entire surface of the MaterialLayers will result in the layers being combined.

>>> layers.add(1., type=3., size='sand')
>>> layers.add([2, -1, 0], type=3., size='sand')
>>> layers.dz
array([[ 4.,  1.,  2.]])


Adding material with different attributes results in the creation of a new layer.

>>> layers.add(2., type=6., size='sand')
>>> layers.dz
array([[ 4.,  1.,  2.],
[ 2.,  2.,  2.]])
>>> layers['type']
array([[ 3.,  3.,  3.],
[ 6.,  6.,  6.]])
>>> np.all(layers['size'] == [['sand', 'sand', 'sand'],
...                           ['sand', 'sand', 'sand']])
True


Attributes for each layer will exist even if part the the layer is associated with erosion.

>>> layers.add([-2, -1, 1], type=8., size='gravel')
>>> layers.dz
array([[ 4.,  1.,  2.],
[ 0.,  1.,  2.],
[ 0.,  0.,  1.]])
>>> layers['type']
array([[ 3.,  3.,  3.],
[ 6.,  6.,  6.],
[ 8.,  8.,  8.]])


To get the values at the surface of the layer stack:

>>> layers.get_surface_values('type')
array([ 3.,  6.,  8.])


Removing enough material such that an entire layer’s thickness is no longer present, results in that layer no longer being tracked. This is another difference between MaterialLayers and EventLayers.

>>> layers.add([ 0., 0., -1. ])
>>> layers.dz
array([[ 4.,  1.,  2.],
[ 0.,  1.,  2.]])
>>> layers['type']
array([[ 3.,  3.,  3.],
[ 6.,  6.,  6.]])
>>> np.all(layers['size'] == [['sand', 'sand', 'sand'],
...                           ['sand', 'sand', 'sand']])
True
>>> layers.number_of_layers
2


If attributes (like age and size in this example) are tracked, a layer will be combined with the surface layer only if all attributes are the same across the entire layer. Right now, the surface values vary.

>>> layers.get_surface_values('type')
array([ 3.,  6.,  6.])
>>> np.all(layers.get_surface_values('size') == ['sand', 'sand', 'sand'])
True


Since the surface has different types, adding material will create a new layer.

>>> layers.add(3., type=6., size='sand')
>>> layers.dz
array([[ 4.,  1.,  2.],
[ 0.,  1.,  2.],
[ 3.,  3.,  3.]])
>>> layers['type']
array([[ 3.,  3.,  3.],
[ 6.,  6.,  6.],
[ 6.,  6.,  6.]])
>>> layers.number_of_layers
3


But now, the entire surface has the qualities of type = 6. and size = ‘sand’, so layers will be combined. This even works if the thickness of the new layer includes both erosion and deposition.

>>> layers.add([ -3.5, 0., 2. ], type=6., size='sand')
>>> layers.dz
array([[ 3.5,  1. ,  2. ],
[ 0. ,  1. ,  2. ],
[ 0. ,  3. ,  5. ]])
>>> layers['type']
array([[ 3.,  3.,  3.],
[ 6.,  6.,  6.],
[ 6.,  6.,  6.]])
>>> layers.number_of_layers
3

is_compatible(dz, **kwds)[source]

Check if a new layer is compatible with the existing top layer.

Parameters: dz (float or array_like) – Thickness to add to each stack. True if the new layer is compatible, otherwise False. bool
class MaterialLayersMixIn[source]

Bases: object

MixIn that adds a MaterialLayers attribute to a ModelGrid.

material_layers

MaterialLayers for each cell.