#!/usr/bin/env python
# coding: utf-8

# # 활성화 함수 (Activation Function)

# ## 1. 시그모이드 함수 (Sigmoid Function)

# In[2]:


import numpy as np
import matplotlib.pylab as plt


# In[3]:


def sigmoid(x):
    return 1 / (1 + np.exp(-x))    

X = np.arange(-5.0, 5.0, 0.1)
Y = sigmoid(X)
plt.plot(X, Y)
plt.ylim(-0.1, 1.1)
plt.show()


# ## 2 계단 함수 (Step Function)

# In[4]:


def step_function(x):
    y = x > 0
    return y.astype(dtype=np.int)

X = np.arange(-5.0, 5.0, 0.1)
Y = step_function(X)
plt.plot(X, Y)
plt.ylim(-0.1, 1.1)
plt.show()


# In[5]:


def sigmoid(x):
    return 1 / (1 + np.exp(-x))    

def step_function(x):
    return np.array(x > 0, dtype=np.int)

x = np.arange(-5.0, 5.0, 0.1)
y1 = sigmoid(x)
y2 = step_function(x)

plt.plot(x, y1)
plt.plot(x, y2, 'k--')
plt.ylim(-0.1, 1.1)
plt.show()


# ## 3. ReLU 함수 (Rectified Linear Unit Function)

# In[6]:


def relu(x):
    return np.maximum(0, x)

x = np.arange(-5.0, 5.0, 0.1)
y = relu(x)
plt.plot(x, y)
plt.ylim(-1.0, 5.5)
plt.show()


# ## 4. 소프트맥스 함수 (Softmax Function)

# In[21]:


def softmax_(x):
    exp_x = np.exp(x)
    sum_exp_x = np.sum(exp_x)
    y = exp_x / sum_exp_x
    return y

def softmax(x):
    c = np.max(x)
    exp_x = np.exp(x-c)
    sum_exp_x = np.sum(exp_x)
    y = exp_x / sum_exp_x
    return y

x = np.array([0.3, 2.9, 4.0])
y = softmax(x)
print(x)
print(y)
print("np.sum(y):", np.sum(y))


# ## 5. 항등 함수 (Identity Function)

# In[23]:


def identity(x):
    return x

x = np.arange(-5.0, 5.0, 0.1)
y = identity(x)
plt.plot(x, y)
plt.ylim(-5.5, 5.5)
plt.show()