update comment for ch07

.gitignore

@@ -5,6 +5,7 @@
 *~
 .#*
 *.dot
+*.svg
 *.png
 *.zip
 *.lprof

ch07_autograd/README.md

@@ -0,0 +1,15 @@
+
+|代码|说明|
+|---|---|
+|[utils.py](utils.py)| 定义Scalar类以及相应的可视化工具 |
+|[linear_model.py](linear_model.py)| 定义线性回归模型 |
+|[autograd.ipynb](autograd.ipynb)| 通过简单的例子，展示向前传播和反向传播的过程 |
+|[optim_process.ipynb](optim_process.ipynb)| 展示在模型训练过程中出现的计算图膨胀现象，以及如何利用反向传播算法训练线性回归模型 |
+|[gradient_accumulation.ipynb](gradient_accumulation.ipynb)| 梯度累积算法 |
+|[parameter_freezing.ipynb](parameter_freezing.ipynb)| 参数冻结 |
+|[dropout.ipynb](dropout.ipynb)| 随机失活 |
+|[gpu.ipynb](gpu.ipynb)| GPU运算 |
+
+
+
+

ch07_autograd/autograd.ipynb

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-      "Requirement already satisfied: pygraphviz in /Users/tgbaggio/opt/anaconda3/lib/python3.8/site-packages (1.11)\r\n"
-     ]
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-   ],
+   "outputs": [],
    "source": [
+    "# 安装第三方库\n",
     "!pip install pygraphviz"
    ]
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-       "<g id=\"node5\" class=\"node\"><title>4416480400backward</title>\n",
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      "execution_count": 5,
@@ -360,7 +353,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "# 将反向传播的过程展示出来\n",
+    "# 将反向传播的过程展示出来（可能会有弹框）\n",
     "for index, pic in enumerate(backward_process):\n",
     "    pic.view(str(index))"
    ]

ch07_autograd/dropout.ipynb

@@ -219,10 +219,12 @@
     }
    ],
    "source": [
+    "# 定义训练数据\n",
     "x1 = Scalar(1.5, label='x1', requires_grad=False)\n",
     "y1 = Scalar(1.0, label='y1', requires_grad=False)\n",
     "x2 = Scalar(2.0, label='x2', requires_grad=False)\n",
     "y2 = Scalar(4.0, label='y2', requires_grad=False)\n",
+    "# 定义正常的计算图\n",
     "model = Linear()\n",
     "k = model.forward(x1)\n",
     "l = y1 - k\n",

ch07_autograd/gradient_accumulation.ipynb

@@ -219,6 +219,7 @@
     }
    ],
    "source": [
+    "# 定义训练数据\n",
     "x1 = Scalar(1.5, label='x1', requires_grad=False)\n",
     "y1 = Scalar(1.0, label='y1', requires_grad=False)\n",
     "x2 = Scalar(2.0, label='x2', requires_grad=False)\n",
@@ -391,7 +392,7 @@
     "# 梯度累积\n",
     "model = Linear()\n",
     "# 使用x1，y1传播一次\n",
-    "# 系数0.5是因为平均数权重调整\n",
+    "# 系数0.5是因为梯度累积2次\n",
     "loss = 0.5 * mse([model.error(x1, y1)])\n",
     "loss.backward()\n",
     "draw_graph(loss, 'backward')"
@@ -618,6 +619,7 @@
     "batch_size = 20\n",
     "# 定义每批次梯度累积的次数\n",
     "gradient_accumulation_iter = 4\n",
+    "# 每次反向传播的数据量\n",
     "micro_size = int(batch_size / gradient_accumulation_iter)\n",
     "learning_rate = 0.1\n",
     "\n",
@@ -628,6 +630,7 @@
     "    yy = y[ix: ix + micro_size]\n",
     "    # 计算当前批次数据的损失\n",
     "    loss = mse([model.error(_x, _y) for _x, _y in zip(xx, yy)])\n",
+    "    # 根据梯度累积的次数，调整模型损失的权重\n",
     "    loss *= 1 / gradient_accumulation_iter\n",
     "    # 计算损失函数的梯度\n",
     "    loss.backward()\n",

ch07_autograd/linear_model.py

@@ -1,16 +1,16 @@
 # -*- coding: UTF-8 -*-
-"""
+'''
 此脚本用于定义线性回归模型
-"""
+'''
 
 
 from utils import Scalar
 
 
 def mse(errors):
-    """
+    '''
     计算均方误差
-    """
+    '''
     n = len(errors)
     wrt = {}
     value = 0.0
@@ -26,27 +26,28 @@ def mse(errors):
 
 
 class Linear:
+    
     def __init__(self):
-        """
+        '''
         定义线性回归模型的参数：a, b
-        """
+        '''
         self.a = Scalar(0.0, label='a')
         self.b = Scalar(0.0, label='b')
 
     def forward(self, x):
-        """
+        '''
         根据当前的参数估计值，得到模型的预测结果
-        """
+        '''
         return self.a * x + self.b
     
     def error(self, x, y):
-        """
+        '''
         当前数据的模型误差
-        """
+        '''
         return y - self.forward(x)
 
     def string(self):
-        """
+        '''
         输出当前模型的结果
-        """
+        '''
         return f'y = {self.a.value:.2f} * x + {self.b.value:.2f}'

ch07_autograd/optim_process.ipynb

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    "source": [
     "# 计算图膨胀\n",
     "model = Linear()\n",
+    "# 定义训练数据\n",
     "x1 = Scalar(1.5, label='x1', requires_grad=False)\n",
     "y1 = Scalar(1.0, label='y1', requires_grad=False)\n",
     "x2 = Scalar(2.0, label='x2', requires_grad=False)\n",
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       "text/plain": [
-       "<graphviz.graphs.Digraph at 0x10d5bb9d0>"
+       "<graphviz.graphs.Digraph at 0x7fe0ee8ec670>"
       ]
      },
      "execution_count": 4,

ch07_autograd/parameter_freezing.ipynb

@@ -219,6 +219,7 @@
     }
    ],
    "source": [
+    "# 定义训练数据\n",
     "x1 = Scalar(1.5, label='x1', requires_grad=False)\n",
     "y1 = Scalar(1.0, label='y1', requires_grad=False)\n",
     "x2 = Scalar(2.0, label='x2', requires_grad=False)\n",

ch07_autograd/utils.py

@@ -1,7 +1,7 @@
 # -*- coding: UTF-8 -*-
-"""
+'''
 此脚本用于定义Scalar类，以及相应的可视化工具
-"""
+'''
 
 
 from graphviz import Digraph
@@ -9,17 +9,18 @@ import math
 
 
 class Scalar:
+    
     def __init__(self, value, prevs=[], op=None, label='', requires_grad=True):
         # 节点的值
         self.value = value
         # 节点的标识（label）和对应的运算（op），用于作图
         self.label = label
         self.op = op
-        # 节点的前节点
+        # 节点的前节点，即当前节点是运算的结果，而前节点是参与运算的量
         self.prevs = prevs
-        # 是否需要计算该节点偏导数，即∂loss/∂self
+        # 是否需要计算该节点偏导数，即∂loss/∂self（loss表示最后的模型损失）
         self.requires_grad = requires_grad
-        # 存储该节点偏导数，即∂loss/∂self
+        # 该节点偏导数，即∂loss/∂self
         self.grad = 0.0
         # 如果该节点的prevs非空，存储所有的∂self/∂prev
         self.grad_wrt = dict()
@@ -30,9 +31,9 @@ class Scalar:
         return f'Scalar(value={self.value:.2f}, grad={self.grad:.2f})'
     
     def __add__(self, other):
-        """
+        '''
         定义加法，self + other将触发该函数
-        """
+        '''
         if not isinstance(other, Scalar):
             other = Scalar(other, requires_grad=False)
         # output = self + other
@@ -45,9 +46,9 @@ class Scalar:
         return output
     
     def __sub__(self, other):
-        """
+        '''
         定义减法，self - other将触发该函数
-        """
+        '''
         if not isinstance(other, Scalar):
             other = Scalar(other, requires_grad=False)
         # output = self - other
@@ -60,9 +61,9 @@ class Scalar:
         return output
     
     def __mul__(self, other):
-        """
+        '''
         定义乘法，self * other将触发该函数
-        """
+        '''
         if not isinstance(other, Scalar):
             other = Scalar(other, requires_grad=False)
         # output = self * other
@@ -75,10 +76,10 @@ class Scalar:
         return output
     
     def __pow__(self, other):
-        """
+        '''
         定义乘方，self**other将触发该函数
-        """
-        assert isinstance(other, (int, float)), 'support only int or float in the exponent'
+        '''
+        assert isinstance(other, (int, float))
         # output = self ** other
         output = Scalar(self.value ** other, [self], f'^{other}')
         output.requires_grad = self.requires_grad
@@ -87,9 +88,9 @@ class Scalar:
         return output
     
     def sigmoid(self):
-        """
+        '''
         定义sigmoid
-        """
+        '''
         s = 1 / (1 + math.exp(-1 * self.value))
         output = Scalar(s, [self], 'sigmoid')
         output.requires_grad = self.requires_grad
@@ -98,43 +99,45 @@ class Scalar:
         return output
     
     def __rsub__(self, other):
-        """
+        '''
         定义右减法，other - self将触发该函数
-        """
+        '''
         if not isinstance(other, Scalar):
             other = Scalar(other, requires_grad=False)
         output = Scalar(other.value - self.value, [self, other], '-')
         output.requires_grad = self.requires_grad or other.requires_grad
+        # 计算偏导数 ∂output/∂self = -1
         output.grad_wrt[self] = -1
+        # 计算偏导数 ∂output/∂other = 1
         output.grad_wrt[other] = 1
         return output
     
     def __radd__(self, other):
-        """
+        '''
         定义右加法，other + self将触发该函数
-        """
+        '''
         return self.__add__(other)
     
     def __rmul__(self, other):
-        """
+        '''
         定义右乘法，other * self将触发该函数
-        """
+        '''
         return self * other
     
     def backward(self, fn=None):
-        """
-        由当前节点出发，求解以当前节点为顶点的计算图中每个节点的梯度，i.e. ∂self/∂node
+        '''
+        由当前节点出发，求解以当前节点为顶点的计算图中每个节点的偏导数，i.e. ∂self/∂node
         参数
         ----
         fn ：画图函数，如果该变量不等于None，则会返回向后传播每一步的计算的记录
         返回
         ----
         re ：向后传播每一步的计算的记录
-        """
+        '''
         def _topological_order():
-            """
+            '''
             利用深度优先算法，返回计算图的拓扑排序（topological sorting）
-            """
+            '''
             def _add_prevs(node):
                 if node not in visited:
                     visited.add(node)
@@ -146,9 +149,9 @@ class Scalar:
             return ordered
 
         def _compute_grad_of_prevs(node):
-            """
+            '''
             由node节点出发，向后传播
-            """
+            '''
             # 作图需要，实际上对计算没有作用
             node.back_prop = dict()
             # 得到当前节点在计算图中的梯度。由于一个节点可以在多个计算图中出现，
@@ -157,8 +160,8 @@ class Scalar:
             # 使用node.grad记录节点的累积梯度
             node.grad += dnode
             for prev in node.prevs:
-                # 由于node节点的偏导数已经计算完成，可以向后传播
-                # 需要注意的是，向后传播到上游节点是累加关系
+                # 由于node节点的偏导数已经计算完成，可以向后扩散（反向传播）
+                # 需要注意的是，向后扩散到上游节点是累加关系
                 grad_spread = dnode * node.grad_wrt[prev]
                 cg_grad[prev] = cg_grad.get(prev, 0.0) + grad_spread
                 node.back_prop[prev] = node.back_prop.get(prev, 0.0) + grad_spread
@@ -177,9 +180,9 @@ class Scalar:
 
 
 def _get_node_attr(node, direction='forward'):
-    """
+    '''
     节点的属性
-    """
+    '''
     node_type = _get_node_type(node)
     def _forward_attr():
         if node_type == 'param':
@@ -200,7 +203,8 @@ def _get_node_attr(node, direction='forward'):
         attr['label'] = attr['label'].replace('grad=None', f'grad={node.grad: .2f}')
         if not node.requires_grad:
             attr['style'] = 'dashed'
-        # 如果向后传播的梯度要么等于0，要么传给不需要梯度的节点，那么该节点用虚线表示
+        # 为了作图美观
+        # 如果向后扩散（反向传播）的梯度等于0，或者扩散给不需要梯度的节点，那么该节点用虚线表示
         grad_back = [v if k.requires_grad else 0 for (k, v) in node.back_prop.items()]
         if len(grad_back) > 0 and sum(grad_back) == 0:
             attr['style'] = 'dashed'
@@ -213,9 +217,9 @@ def _get_node_attr(node, direction='forward'):
     
     
 def _get_node_type(node):
-    """
+    '''
     决定节点的类型，计算节点、参数以及输入数据
-    """
+    '''
     if node.op is not None:
         return 'computation'
     if node.requires_grad:
@@ -224,9 +228,9 @@ def _get_node_type(node):
 
 
 def _trace(root):
-    """
+    '''
     遍历图中的所有点和边
-    """
+    '''
     nodes, edges = set(), set()
     def _build(v):
         if v not in nodes:
@@ -239,18 +243,18 @@ def _trace(root):
 
 
 def _draw_node(graph, node, direction='forward'):
-    """
+    '''
     画节点
-    """
+    '''
     node_attr = _get_node_attr(node, direction)
     uid = str(id(node)) + direction
     graph.node(name=uid, **node_attr)
 
 
 def _draw_edge(graph, n1, n2, direction='forward'):
-    """
+    '''
     画边
-    """
+    '''
     uid1 = str(id(n1)) + direction
     uid2 = str(id(n2)) + direction
     def _draw_back_edge():
@@ -275,7 +279,7 @@ def _draw_edge(graph, n1, n2, direction='forward'):
 
 
 def draw_graph(root, direction='forward'):
-    """
+    '''
     图形化展示由root为顶点的计算图
     参数
     ----
@@ -284,7 +288,7 @@ def draw_graph(root, direction='forward'):
     返回
     ----
     re ：Digraph，计算图
-    """
+    '''
     nodes, edges = _trace(root)
     rankdir = 'BT' if direction == 'forward' else 'TB'
     graph = Digraph(format='svg', graph_attr={'rankdir': rankdir})