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import math
class Scalar:
def __init__(self, data, _children=(), _op='', label='') -> None:
self.label = label
self.data = float(data)
self.grad = 0.0
self._prev = set(_children)
self._op = _op
self._backward = lambda: None
def __repr__(self) -> str:
return f'Scalar({self.label}: {self.data})'
def __add__(self, y):
result = Scalar(self.data + y.data, (self, y), _op='+')
def _backward():
self.grad = result.grad
y.grad = result.grad
self._backward = _backward
return result
def __mul__(self, y):
result = Scalar(self.data * y.data, (self, y), _op='*')
def _backward():
self.grad = y.data * result.grad
y.grad = self.data * result.grad
self._backward = _backward
return result
def tanh(self):
x = self.data
t = (math.exp(2 * x) - 1) / (math.exp(2 * x) + 1)
result = Scalar(t, (self, ), 'tanh')
def _backward():
self.grad = (1 - (t ** 2)) * result.grad
self._backward = _backward
return result
def build_children(self):
result = []
result.append(self)
for child in self._prev:
result += child.build_children()
return result
def backward(self):
self.grad = 1.0
children = self.build_children()
for child in children:
child._backward()
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