“深度学习”学习日记。误差反向传播法--加法层、乘法层、激活函数层的实现

2023.1.16

前两篇文章都在讲述理论，今天实现代码操作：关于加法节点，乘法节点的内容在这篇文章。

https://blog.youkuaiyun.com/m0_72675651/article/details/128695488

在以后的学习中，将把构建神经网络的“层”实现为一个类。这里的“层”是指神经网络中功能的单位。

这样写感觉到可以让代码变得美观一点，而更容易找出错误并修改

class Addyer:  # 加法节点
    def __init__(self):
        pass

    def forward(self, x, y):
        out = x + y
        return out

    def backward(self, dout):
        dx = dout * 1
        dy = dout * 1
        return dx, dy


class Mullyer:  # 乘法节点
    def __init__(self):  # __init__() 中会初始化实例变量
        self.x = None
        self.y = None

    def forward(self, x, y):
        self.x = y
        self.y = x
        out = x * y

        return out

    def backward(self, dout):
        dx = dout * self.x
        dy = dout * self.y

        return dx, dy

现在用代码实现了，加法层和乘法层，所以我们用代码解决这个问题：

利用反向传播法，求解，篮球、足球分别对应付金额上涨1元的影响是多少？

 

 代码实现：

class Addyer:  # 加法节点
    def __init__(self):
        pass

    def forward(self, x, y):
        out = x + y
        return out

    def backward(self, dout):
        dx = dout * 1
        dy = dout * 1
        return dx, dy


class Mullyer:  # 乘法节点
    def __init__(self):  # __init__() 中会初始化实例变量
        self.x = None
        self.y = None

    def forward(self, x, y):
        self.x = y
        self.y = x
        out = x * y

        return out

    def backward(self, dout):
        dx = dout * self.x
        dy = dout * self.y

        return dx, dy


discout = 0.9

basketball = 100  # b
football = 200  # f

basketball_num = 2
footbal_num = 3

# 求解问题时 因为乘法层的反向传播需要正向传播的参数
m = Mullyer()
m1 = Mullyer()
m2 = Mullyer()
a = Addyer()

b_price = m2.forward(basketball, basketball_num)
f_price = m1.forward(football, footbal_num)
b_f_price = a.forward(b_price, f_price)
final_price = m.forward(discout, b_f_price)

print(final_price)  # 720
# 求解 应付金额上涨1元 delta=1
# 篮球得影响
delta = 1
ddiscount, db_f_price = m.backward(delta)
dbaskbetball1, dfootball1 = a.backward(db_f_price)
dbaskbetball, dbaskbetball_num = m2.backward(dbaskbetball1)
dfootball, dfootball_num = m1.backward(dfootball1)

print(db_f_price)  # 800
print(dfootball1)  # 0.9
print(dbaskbetball, dbaskbetball_num)  # 1.8 90.0
print(dfootball, dfootball_num)  # 2.7 180.0