各种导数（梯度）下降优化算法python实现

阅读更多

梯度下降算法总纲：

1：CS231

http://cs231n.github.io/neural-networks-3/

https://zhuanlan.zhihu.com/p/21798784?refer=intelligentunit

 

2:An overview of gradient descent optimization algorithms

http://ruder.io/optimizing-gradient-descent/index.html

 

 

ADADELTA: AN ADAPTIVE LEARNING RATE METHOD

https://arxiv.org/pdf/1212.5701.pdf

 

ADAM: A METHOD FOR STOCHASTIC OPTIMIZATION

https://arxiv.org/pdf/1412.6980.pdf

 

 

一般的梯度下降法：

核心就是   learning_rate * gradient

def f(x):
        return x**3-2*x - 10 +x**2

def derivative_f(x):
         return 3*(x**2)+2*-2


x=0.0
y=0.0
learning_rate = 0.001
gradient=0

for i in range(1000000):
        print('x = {:6f}, f(x) = {:6f},gradient={:6f}'.format(x,y,gradient))

        if((abs(gradient)>0.00001) and (abs(gradient)<0.0001)):
            print("break at "+str(i))
            break
        else:
            gradient = derivative_f(x)
            x = x -  learning_rate*gradient
            y = f(x)

 

 ADAGRAD 实现（按照文档上的收敛很差，所以修改了分母）

核心是 learning_rate*gradient/(math.sqrt(sum/(i+1))+e)

 

import math
def f(x):
        return x**3-2*x - 10 +x**2

def derivative_f(x):
         return 3*(x**2)+2*-2


x=0.0
y=0.0
learning_rate = 0.001
gradient=0
e=0.00000001
sum = 0.0

for i in range(100000):

    print('x = {:6f}, f(x) = {:6f},gradient={:6f}'.format(x,y,gradient))
    if((abs(gradient)>0.00001) and (abs(gradient)<0.0001)):
            print("break at "+str(i))
            break
    else:
        gradient = derivative_f(x)
        sum += gradient**2;
        x=x-learning_rate*gradient/(math.sqrt(sum/(i+1))+e)
        y=f(x)

 

ADADELTA实现

import math
def f(x):
        return x**3-2*x - 10 +x**2

def derivative_f(x):
         return 3*(x**2)+2*-2


x=0.0
y=0.0
learning_rate = 0.001
gradient=0
e=0.00000001
sum = 0.0

d = 0.9

Egt=0
Edt = 0


delta = 0

for i in range(100000):

    print('x = {:6f}, f(x) = {:6f},gradient={:6f}'.format(x,y,gradient))
    if(abs(gradient)>0.00001 and (abs(gradient)<0.0001)):
        print("break at "+str(i))
        break
    else:

        gradient = derivative_f(x)

        Egt = d * Egt + (1-d)*(gradient**2)

        delta = math.sqrt(Edt + e)*gradient/math.sqrt(Egt + e)

        Edt = d*Edt+(1-d)*(delta**2)

        x=x-delta
        y = f(x)

 

RMSprop实现

import math
def f(x):
        return x**3-2*x - 10 +x**2

def derivative_f(x):
         return 3*(x**2)+2*-2


x=0.0
y=0.0
learning_rate = 0.001
gradient=0
e=0.00000001
sum = 0.0

d = 0.9

Egt=0
Edt = 0


delta = 0

for i in range(100000):

    print('x = {:6f}, f(x) = {:6f},gradient={:6f}'.format(x,y,gradient))
    if(abs(gradient)>0.00001 and (abs(gradient)<0.0001)):
        print("break at "+str(i))
        break
    else:

        gradient = derivative_f(x)

        Egt = d * Egt + (1-d)*(gradient**2)

        x=x-learning_rate*gradient/math.sqrt(Egt + e)

        y=f(x)

 

Adam 实现

import math
def f(x):
        return x**3-2*x - 10 +x**2

def derivative_f(x):
         return 3*(x**2)+2*-2


x=0.0
y=0.0
learning_rate = 0.001
gradient=0
e=0.00000001

b1 = 0.9
b2 = 0.995

m = 0
v = 0
t = 0

for i in range(10000):


    print('x = {:6f}, f(x) = {:6f},gradient={:6f}'.format(x,y,gradient))
    if(abs(gradient)>0.00001 and (abs(gradient)<0.0001)):
        print("break at "+str(i))
        break
    else:

        gradient = derivative_f(x)

        t=t+1

        'mt ← β1 · mt−1 + (1 − β1) · gt '
        m = b1*m + (1-b1)*gradient

        'vt ← β2 · vt−1 + (1 − β2) · g2'
        v = b2*v +(1-b2)*(gradient**2)

        'mt ← mt/(1 − βt1)'
        mt = m/(1-(b1**t))

        'vbt ← vt/(1 − βt2)'
        vt = v/(1-(b2**t))


        x = x- learning_rate * mt/(math.sqrt(vt)+e)

        y=f(x)

 

总体感觉RMSprop 最优