Guide

• Start
• Modules
  • Nodes
  • Tree
• Usage

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Start

This is a library to create decision trees and calculate the expected value of the best strategy.

To install the library, run the following command:

pip install precision-tree

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Modules

The library has two main modules: nodes and tree.

The nodes module contains the classes to create the nodes of the decision tree. The tree module contains the class to wrap the root node and calculate the expected value of the best strategy and visualize the tree.

Nodes

The nodes module contains the following classes:

• DecisionNode: Represents a decision node.

• ChanceNode: Represents a chance node.

• PayoffNode: Represents a payoff node.

All of the classes are subclasses of the Node class.

DecisionNode

The DecisionNode class represents a decision node (in graph it looks like a squere).

The following table shows the attributes of the DecisionNode class:

Attribute	Description
name	The name of the node.
branches	A list of branches.

The following table shows the methods of the DecisionNode class:

Method	Description
add_branch(self, label, child)	Adds a branch to the node. label is the name of the branch and child is the child node.
calculate_value	Calculates the expected value of the best strategy.

ChanceNode

The ChanceNode class represents a chance node (in graph it looks like a circle).

The following table shows the attributes of the ChanceNode class:

Attribute	Description
name	The name of the node.
cost	The cost of the node.
years	The number of years.
branches	A list of branches.

The following table shows the methods of the ChanceNode class:

Method	Description
add_branch(self, label, child, probability)	Adds a branch to the node. label is the name of the branch, child is the child node, and probability is the probability of the branch.
calculate_value	Calculates the expected value of the best strategy.

PayoffNode

The PayoffNode class represents a payoff node (in graph it looks like a triangle).

The following table shows the attributes of the PayoffNode class:

Attribute	Description
name	The name of the node.
value	The value of the node.
branches	A list of branches.

The following table shows the methods of the PayoffNode class:

Method	Description
calculate_value	Calculates the expected value of the best strategy.

Tree

The tree module contains the TreeWrapper class.

The following table shows the attributes of the TreeWrapper class:

Attribute	Description
root	The root node of the tree.

The following table shows the methods of the TreeWrapper class:

Method	Description
show(self, title: str, format: str):	Shows the tree. title is the title of the tree and format is the format of the file png, pdf etc.
get_optimal_path	Returns the optimal path as a tuple, where the first element is the optimal nodes and second element is the optimal edges.
calculate_value	Calculates the expected value of the best strategy.

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Usage

Example

from precision_tree.nodes import DecisionNode, ChanceNode, PayoffNode
from precision_tree.tree import TreeWrapper


root = DecisionNode("Decision")

# Decision Node Without Analytics
without_analytics = DecisionNode("Without Analytics")

big_factory = ChanceNode("Big Factory 1", cost=0, years=1)
big_factory.add_branch(label="Favorable P(0.7)", child=PayoffNode("Favorable 1", 200), probability=0.7)
big_factory.add_branch(label="Unfavorable P(0.3)", child=PayoffNode("Unfavorable 1", -180), probability=0.3)

small_factory = ChanceNode("Small Factory 1", cost=0, years=1)
small_factory.add_branch(label="Favorable P(0.7)", child=PayoffNode("Favorable 2", 100), probability=0.7)
small_factory.add_branch(label="Unfavorable P(0.3)", child=PayoffNode("Unfavorable 2", -20), probability=0.3)

without_analytics.add_branch(label="Big Factory", child=big_factory)
without_analytics.add_branch(label="Small Factory", child=small_factory)
without_analytics.add_branch(label="Sell Patent", child=PayoffNode("Sell Patent 1", 10))

# Make Decision Node With Analytics
with_analytics = ChanceNode("With Analytics", cost=8, years=1)

# Positive Result
positive_result = DecisionNode("Positive Result")

big_factory_positive = ChanceNode("Big Factory 2", cost=0, years=1)
big_factory_positive.add_branch(label="Favorable", child=PayoffNode("Favorable 3", 200), probability=0.81)
big_factory_positive.add_branch(label="Unfavorable", child=PayoffNode("Unfavorable 3", -180), probability=0.19)

small_factory_positive = ChanceNode("Small Factory 2", cost=0, years=1)
small_factory_positive.add_branch(label="Favorable", child=PayoffNode("Favorable 4", 100), probability=0.81)
small_factory_positive.add_branch(label="Unfavorable", child=PayoffNode("Unfavorable 4", -20), probability=0.19)

positive_result.add_branch(label="Big Factory", child=big_factory_positive)
positive_result.add_branch(label="Small Factory", child=small_factory_positive)
positive_result.add_branch(label="Sell Patent", child=PayoffNode("Sell Patent 2", 10))

# Negative Result
negative_result = DecisionNode("Negative Result")

big_factory_negative = ChanceNode("Big Factory 3", cost=0, years=1)
big_factory_negative.add_branch(label="Favorable", child=PayoffNode("Favorable 5", 200), probability=0.28)
big_factory_negative.add_branch(label="Unfavorable", child=PayoffNode("Unfavorable 5", -180), probability=0.72)

small_factory_negative = ChanceNode("Small Factory 3", cost=0, years=1)
small_factory_negative.add_branch(label="Favorable", child=PayoffNode("Favorable 6", 100), probability=0.28)
small_factory_negative.add_branch(label="Unfavorable", child=PayoffNode("Unfavorable 6", -20), probability=0.72)

negative_result.add_branch(label="Big Factory", child=big_factory_negative)
negative_result.add_branch(label="Small Factory", child=small_factory_negative)
negative_result.add_branch(label="Sell Patent", child=PayoffNode("Sell Patent 3", 10))

with_analytics.add_branch(label="Positive Result", child=positive_result, probability=0.48)
with_analytics.add_branch(label="Negative Result", child=negative_result, probability=0.52)

# Add Branches to Root
root.add_branch(label="With Analytics", child=with_analytics)
root.add_branch(label="Without Analytics", child=without_analytics)

tree = TreeWrapper(root)
print(f"Expected Value of the best strategy: {tree.calculate_value():.2f}")
print(f"Optimal branch: {tree.get_optimal_path()[0]}")

Output

Expected Value of the best strategy: 86.00
Optimal branch: {'Unfavorable 1', 'Favorable 1', 'Big Factory 1', 'Without Analytics', 'Decision'}