05_CartPole-reinforcement-learning_PER_D3QN

SumTree___init__.py

class SumTree(object):
    data_pointer = 0
    
    # Here we initialize the tree with all nodes = 0, and initialize the data with all values = 0
    def __init__(self, capacity):
        # Number of leaf nodes (final nodes) that contains experiences
        self.capacity = capacity
        
        # Generate the tree with all nodes values = 0
        # To understand this calculation (2 * capacity - 1) look at the schema below
        # Remember we are in a binary node (each node has max 2 children) so 2x size of leaf (capacity) - 1 (root node)
        # Parent nodes = capacity - 1
        # Leaf nodes = capacity
        self.tree = np.zeros(2 * capacity - 1)
        
        # Contains the experiences (so the size of data is capacity)
        self.data = np.zeros(capacity, dtype=object)