API

The PGM Object

All daft scripts will start with the creation of a PGM object. This object contains a list of Node objects and Edge objects connecting them. You can also specify rendering parameters and other default parameters when you initialize your PGM.

class daft.PGM(shape=None, origin=None, grid_unit=2.0, node_unit=1.0, observed_style='shaded', alternate_style='inner', line_width=1.0, node_ec='k', directed=True, aspect=1.0, label_params={}, dpi=None)

The base object for building a graphical model representation.

Parameters:
  • shape – (optional) The number of rows and columns in the grid. Will automatically determine is not provided.
  • origin – (optional) The coordinates of the bottom left corner of the plot. Will automatically determine if not provided.
  • grid_unit – (optional) The size of the grid spacing measured in centimeters.
  • node_unit – (optional) The base unit for the node size. This is a number in centimeters that sets the default diameter of the nodes.
  • observed_style – (optional) How should the “observed” nodes be indicated? This must be one of: "shaded", "inner" or "outer" where inner and outer nodes are shown as double circles with the second circle plotted inside or outside of the standard one, respectively.
  • alternate_style – (optional) How should the “alternate” nodes be indicated? This must be one of: "shaded", "inner" or "outer" where inner and outer nodes are shown as double circles with the second circle plotted inside or outside of the standard one, respectively.
  • node_ec – (optional) The default edge color for the nodes.
  • directed – (optional) Should the edges be directed by default?
  • aspect – (optional) The default aspect ratio for the nodes.
  • label_params – (optional) Default node label parameters. See PGM.Node for details.
  • dpi – (optional) Set DPI for display and saving files.
add_edge(name1, name2, directed=None, xoffset=0.0, yoffset=0.1, label=None, plot_params={}, label_params={}, **kwargs)

Construct an Edge between two named Node objects.

Parameters:
  • name1 – The name identifying the first node.
  • name2 – The name identifying the second node. If the edge is directed, the arrow will point to this node.
  • directed – (optional) Should the edge be directed from node1 to node2? In other words: should it have an arrow?
  • label – (optional) A string to annotate the edge.
  • xoffset – (optional) The x-offset from the middle of the arrow to plot the label. Only takes effect if label is defined in plot_params.
  • yoffset – (optional) The y-offset from the middle of the arrow to plot the label. Only takes effect if label is defined in plot_params.
  • plot_params – (optional) A dictionary of parameters to pass to the matplotlib.patches.FancyArrow constructor.
  • label_params – (optional) A dictionary of parameters to pass to the matplotlib.axes.Axes.annotate constructor.
add_node(node, content='', x=0, y=0, scale=1.0, aspect=None, observed=False, fixed=False, alternate=False, offset=[0.0, 0.0], fontsize=None, plot_params={}, label_params=None, shape='ellipse')

Add a Node to the model.

Parameters:
  • node – The plain-text identifier for the nodeself. Can also be the Node to retain backward compatibility.
  • content – The display form of the variable.
  • x – The x-coordinate of the node in model units.
  • y – The y-coordinate of the node.
  • scale – (optional) The diameter (or height) of the node measured in multiples of node_unit as defined by the PGM object.
  • aspect – (optional) The aspect ratio width/height for elliptical nodes; default 1.
  • observed – (optional) Should this be a conditioned variable?
  • fixed – (optional) Should this be a fixed (not permitted to vary) variable? If True, modifies or over-rides diameter, offset, facecolor, and a few other plot_params settings. This setting conflicts with observed.
  • alternate – (optional) Should this use the alternate style?
  • offset – (optional) The (dx, dy) offset of the label (in points) from the default centered position.
  • fontsize – (optional) The fontsize to use.
  • plot_params – (optional) A dictionary of parameters to pass to the matplotlib.patches.Ellipse constructor.
  • label_params – (optional) A dictionary of parameters to pass to the matplotlib.text.Annotation constructor. Any kwargs not used by Annontation get passed to matplotlib.text.Text.
  • shape – (optional) String in {ellipse (default), rectangle} If rectangle, aspect and scale holds for rectangle
add_plate(plate, label=None, label_offset=[5, 5], shift=0, position='bottom left', fontsize=None, rect_params=None, bbox=None)

Add a Plate object to the model.

Parameters:
  • plate – The rectangle describing the plate bounds in model coordinates. Can also be the Plate to retain backward compatibility.
  • label – (optional) A string to annotate the plate.
  • label_offset – (optional) The x and y offsets of the label text measured in points.
  • shift – (optional) The vertical “shift” of the plate measured in model units. This will move the bottom of the panel by shift units.
  • position – (optional) One of "{vertical} {horizontal}" where vertical is "bottom" or "middle" or "top" and horizontal is "left" or "center" or "right".
  • fontsize – (optional) The fontsize to use.
  • rect_params – (optional) A dictionary of parameters to pass to the matplotlib.patches.Rectangle constructor.
add_text(x, y, label, fontsize=None)

A subclass of plate to writing text using grid coordinates. Any **kwargs are passed through to PGM.Plate.

Parameters:
  • x – The x-coordinate of the text in model units.
  • y – The y-coordinate of the text.
  • label – A string to write.
  • fontsize – (optional) The fontsize to use.
render(dpi=None)

Render the Plate, Edge and Node objects in the model. This will create a new figure with the correct dimensions and plot the model in this area.

Parameters:dpi – (optional) The DPI value to use for rendering.
savefig(fname, *args, **kwargs)

Wrapper on matplotlib.Figure.savefig() that sets default image padding using bbox_inchaes = tight. *args and **kwargs are passed to matplotlib.Figure.savefig().

Parameters:
  • fname – The filename to save as.
  • dpi – (optional) The DPI value to use for saving.
show(dpi=None, *args, **kwargs)

Wrapper on PGM.render() that calls matplotlib.show() immediately after.

Parameters:dpi – (optional) The DPI value to use for rendering.

Nodes

class daft.Node(name, content, x, y, scale=1.0, aspect=None, observed=False, fixed=False, alternate=False, offset=[0.0, 0.0], fontsize=None, plot_params={}, label_params=None, shape='ellipse')

The representation of a random variable in a PGM.

Parameters:
  • name – The plain-text identifier for the node.
  • content – The display form of the variable.
  • x – The x-coordinate of the node in model units.
  • y – The y-coordinate of the node.
  • scale – (optional) The diameter (or height) of the node measured in multiples of node_unit as defined by the PGM object.
  • aspect – (optional) The aspect ratio width/height for elliptical nodes; default 1.
  • observed – (optional) Should this be a conditioned variable?
  • fixed – (optional) Should this be a fixed (not permitted to vary) variable? If True, modifies or over-rides diameter, offset, facecolor, and a few other plot_params settings. This setting conflicts with observed.
  • alternate – (optional) Should this use the alternate style?
  • offset – (optional) The (dx, dy) offset of the label (in points) from the default centered position.
  • fontsize – (optional) The fontsize to use.
  • plot_params – (optional) A dictionary of parameters to pass to the matplotlib.patches.Ellipse constructor.
  • label_params – (optional) A dictionary of parameters to pass to the matplotlib.text.Annotation constructor. Any kwargs not used by Annontation get passed to matplotlib.text.Text.
  • shape – (optional) String in {ellipse (default), rectangle} If rectangle, aspect and scale holds for rectangle.
get_frontier_coord(target_xy, ctx, edge)

Get the coordinates of the point of intersection between the shape of the node and a line starting from the center of the node to an arbitrary point. Will throw a SameLocationError if the nodes contain the same x and y coordinates. See the example of rectangle below:

_____________
|            |    ____--X (target_node)
|        __--X----
|     X--    |(return coordinate of this point)
|            |
|____________|
Target_xy:(x float, y float) A tuple of coordinate of target node
render(ctx)

Render the node.

Parameters:ctx – The _rendering_context object.

Edges

class daft.Edge(node1, node2, directed=True, label=None, xoffset=0, yoffset=0.1, plot_params={}, label_params={})

An edge between two Node objects.

Parameters:
  • node1 – The first Node.
  • node2 – The second Node. The arrow will point towards this node.
  • directed – (optional) Should the edge be directed from node1 to node2? In other words: should it have an arrow?
  • label – (optional) A string to annotate the edge.
  • xoffset – (optional) The x-offset from the middle of the arrow to plot the label. Only takes effect if label is defined in plot_params.
  • yoffset – (optional) The y-offset from the middle of the arrow to plot the label. Only takes effect if label is defined in plot_params.
  • plot_params – (optional) A dictionary of parameters to pass to the matplotlib.patches.FancyArrow constructor to adjust edge behavior.
  • label_params – (optional) A dictionary of parameters to pass to the matplotlib.axes.Axes.annotate constructor to adjust label behavior.
render(ctx)

Render the edge in the given axes.

Parameters:ctx – The _rendering_context object.

Plates

class daft.Plate(rect, label=None, label_offset=[5, 5], shift=0, position='bottom left', fontsize=None, rect_params=None, bbox=None)

A plate to encapsulate repeated independent processes in the model.

Parameters:
  • rect – The rectangle describing the plate bounds in model coordinates. This is [x-start, y-start, x-length, y-length].
  • label – (optional) A string to annotate the plate.
  • label_offset – (optional) The x- and y- offsets of the label text measured in points.
  • shift – (optional) The vertical “shift” of the plate measured in model units. This will move the bottom of the panel by shift units.
  • position – (optional) One of "{vertical} {horizontal}" where vertical is "bottom" or "middle" or "top" and horizontal is "left" or "center" or "right".
  • fontsize – (optional) The fontsize to use.
  • rect_params – (optional) A dictionary of parameters to pass to the matplotlib.patches.Rectangle constructor, which defines the properties of the plate.
  • bbox – (optional) A dictionary of parameters to pass to the matplotlib.axes.Axes.annotate constructor, which defines the box drawn around the text.
render(ctx)

Render the plate in the given axes.

Parameters:ctx – The _rendering_context object.

The Rendering Context

class daft._rendering_context(**kwargs)
Parameters:
  • shape – The number of rows and columns in the grid.
  • origin – The coordinates of the bottom left corner of the plot.
  • grid_unit – The size of the grid spacing measured in centimeters.
  • node_unit – The base unit for the node size. This is a number in centimeters that sets the default diameter of the nodes.
  • observed_style – How should the “observed” nodes be indicated? This must be one of: "shaded", "inner" or "outer" where inner and outer nodes are shown as double circles with the second circle plotted inside or outside of the standard one, respectively.
  • alternate_style – (optional) How should the “alternate” nodes be indicated? This must be one of: "shaded", "inner" or "outer" where inner and outer nodes are shown as double circles with the second circle plotted inside or outside of the standard one, respectively.
  • node_ec – The default edge color for the nodes.
  • directed – Should the edges be directed by default?
  • aspect – The default aspect ratio for the nodes.
  • label_params – Default node label parameters.
  • dpi – (optional) The DPI value to use for rendering.
convert(*xy)

Convert from model coordinates to plot coordinates.