From 3bc24933f4128e76ccbd6e37155ff6cccb20a182 Mon Sep 17 00:00:00 2001
From: Raghuram Subramani <raghus2247@gmail.com>
Date: Sat, 8 Jun 2024 18:45:09 +0530
Subject: Automate backward propagation

---
 src/graph.py  |  5 +----
 src/scalar.py | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 52 insertions(+), 9 deletions(-)

(limited to 'src')

diff --git a/src/graph.py b/src/graph.py
index 6c8ab53..6bebb06 100644
--- a/src/graph.py
+++ b/src/graph.py
@@ -1,8 +1,5 @@
 import tkinter as tk
-
 from graphviz import Digraph
-import matplotlib.pyplot as plt
-import matplotlib.image as mpimg
 
 from .scalar import Scalar
 
@@ -33,7 +30,7 @@ class Graph:
             # Create a node in the graph
             self.dot.node(
                 name=uid,
-                label=f"{node.label} | {node.data} | grad: {node.grad}",
+                label=f"{node.label} | {node.data:.4f} | grad: {node.grad:.4f}",
                 shape='record'
             )
 
diff --git a/src/scalar.py b/src/scalar.py
index a67b7ae..c8c7601 100644
--- a/src/scalar.py
+++ b/src/scalar.py
@@ -1,3 +1,5 @@
+import math
+
 class Scalar:
     def __init__(self, data, _children=(), _op='', label='') -> None:
         self.label = label
@@ -7,14 +9,58 @@ class Scalar:
 
         self._prev = set(_children)
         self._op = _op
+        
+        self._backward = lambda: None
     
     def __repr__(self) -> str:
-        return f'Scalar({self.data})'
+        return f'Scalar({self.label}: {self.data})'
 
     def __add__(self, y):
-        result = self.data + y.data
-        return Scalar(result, (self, y), _op='+')
+        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 = self.data * y.data
-        return Scalar(result, (self, y), _op='*')
+        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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