pytorch中的Variable

"""
Variable为tensor数据构建计算图，便于网络的运算
"""
import torch
from torch.autograd import Variable

tensor = torch.FloatTensor([[1,2],[3,4]])            # 创建一个tensor类型的数据
variable = Variable(tensor, requires_grad=True)      # 创建一个variable类型的数据

print(tensor)       # [torch.FloatTensor of size 2x2]
print(variable)     # [torch.FloatTensor of size 2x2]

t_out = torch.mean(tensor*tensor)       
v_out = torch.mean(variable*variable) 
print(t_out)
print(v_out)    # 7.5

v_out.backward()    # 从v_out开始反向传播

# 计算谁的梯度，就让开始反向传播的变量对谁进行求导
# v_out = 1/4 * sum(variable*variable)
# the gradients w.r.t the variable, d(v_out)/d(variable) = 1/4*2*variable = variable/2
print(variable.grad)
'''
 0.5000  1.0000
 1.5000  2.0000
'''

print(variable)     # variable格式
"""
Variable containing:
 1  2
 3  4
[torch.FloatTensor of size 2x2]
"""

print(variable.data)    # tensor格式
"""
 1  2
 3  4
[torch.FloatTensor of size 2x2]
"""

print(variable.data.numpy())    # variable是Variable数据类型，variable.data是tensor类型，variable不可转换为numpy类型
"""
[[ 1.  2.]
 [ 3.  4.]]
"""