04wk-1: 딥러닝의 기초 (2)

딥러닝의 기초
Author

최규빈

Published

September 22, 2022

09/22: [딥러닝의 기초] 회귀분석(2)

SSE와 MSE, step1의 다른버전 (torch.nn.Linear)

강의영상

youtube: https://youtube.com/playlist?list=PLQqh36zP38-wezS4h765Rs5mQFoSjrLMk

  • 강의영상 재업로드 하였습니다.

review

import torch
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt 
df = pd.read_csv("https://raw.githubusercontent.com/guebin/DL2022/master/_notebooks/2022-09-22-regression.csv") 
df
x y
0 -2.482113 -8.542024
1 -2.362146 -6.576713
2 -1.997295 -5.949576
3 -1.623936 -4.479364
4 -1.479192 -4.251570
... ... ...
95 2.244400 10.325987
96 2.393501 12.266493
97 2.605604 13.098280
98 2.605658 12.546793
99 2.663240 13.834002

100 rows × 2 columns

x= torch.tensor(df.x,dtype=torch.float32).reshape(100,1)
y= torch.tensor(df.y,dtype=torch.float32).reshape(100,1)
X= torch.tensor([[1]*100,x]).T
What = torch.tensor([[-5.0],[10.0]],requires_grad=True)
What
tensor([[-5.],
        [10.]], requires_grad=True)
plt.plot(x,y,'o')
#plt.plot(x,-5+10*x,'--')
plt.plot(x,X@What.data,'--')

ver1: loss = sum of squares error

alpha = 1/1000
What = torch.tensor([[-5.0],[10.0]],requires_grad=True)
for epoc in range(30): 
    # step1: yhat 
    yhat = X@What 
    # step2: loss 
    loss = torch.sum((y-yhat)**2)
    # step3: 미분 
    loss.backward()
    # step4: update 
    What.data = What.data - alpha * What.grad 
    What.grad = None # 
What
tensor([[2.4290],
        [4.0144]], requires_grad=True)
plt.plot(x,y,'o') 
plt.plot(x,X@What.data,'--')

  • note: 왜 What = What - alpha*What.grad 는 안되는지?

ver2: loss = mean squared error = MSE

alpha = 1/10
What = torch.tensor([[-5.0],[10.0]],requires_grad=True)
for epoc in range(30): 
    # step1: yhat 
    yhat = X@What 
    # step2: loss 
    loss = torch.mean((y-yhat)**2)
    # step3: 미분 
    loss.backward()
    # step4: update 
    What.data = What.data - alpha * What.grad 
    What.grad = None # 
What
tensor([[2.4290],
        [4.0144]], requires_grad=True)

step1의 다른버전: torch.nn.Linear()

ver1: bias=True

torch.manual_seed(43052)
net = torch.nn.Linear(in_features=1, out_features=1, bias=True) 
plt.plot(x,y,'o')
plt.plot(x,net(x).data,'--')

- net에서 \(\hat{w}_0, \hat{w}_1\) 의 값은?

net.weight # w1 
Parameter containing:
tensor([[-0.3467]], requires_grad=True)
net.bias # w0 
Parameter containing:
tensor([-0.8470], requires_grad=True)
_yhat = -0.8470 + -0.3467*x 
plt.plot(x,y,'o')
plt.plot(x, _yhat,'--')
plt.plot(x,net(x).data,'-.')

- 수식표현: \(\hat{y}_i = \hat{w}_0 + \hat{w}_1 x_i = \hat{b} + \hat{w}x_i = -0.8470 + -0.3467 x_i\) for all \(i=1,2,\dots,100\).

ver2

- 입력이 x가 아닌 X를 넣고 싶다면? (보통 잘 안하긴 해요, 왜? bias=False로 주는게 귀찮거든요) - X는 바이어스가 고려된 상황

net(X) ## 그대로 쓰면 당연히 에러
RuntimeError: mat1 and mat2 shapes cannot be multiplied (100x2 and 1x1)
torch.manual_seed(43052)
net = torch.nn.Linear(in_features=2, out_features=1, bias=False) 
net.weight
Parameter containing:
tensor([[-0.2451, -0.5989]], requires_grad=True)
net.bias
plt.plot(x,y,'o') 
plt.plot(x,net(X).data, '--')
plt.plot(x,X@torch.tensor([[-0.2451],[-0.5989]]), '-.')

- 수식표현: \(\hat{\bf y} = {\bf X} {\bf \hat W} = \begin{bmatrix} 1 & x_1 \\ 1 & x_2 \\ \dots & \dots \\ 1 & x_{100} \end{bmatrix} \begin{bmatrix} -0.2451 \\ -0.5989 \end{bmatrix}\)

잘못된사용1

_x = x.reshape(-1)
_x
tensor([-2.4821, -2.3621, -1.9973, -1.6239, -1.4792, -1.4635, -1.4509, -1.4435,
        -1.3722, -1.3079, -1.1904, -1.1092, -1.1054, -1.0875, -0.9469, -0.9319,
        -0.8643, -0.7858, -0.7549, -0.7421, -0.6948, -0.6103, -0.5830, -0.5621,
        -0.5506, -0.5058, -0.4806, -0.4738, -0.4710, -0.4676, -0.3874, -0.3719,
        -0.3688, -0.3159, -0.2775, -0.2772, -0.2734, -0.2721, -0.2668, -0.2155,
        -0.2000, -0.1816, -0.1708, -0.1565, -0.1448, -0.1361, -0.1057, -0.0603,
        -0.0559, -0.0214,  0.0655,  0.0684,  0.1195,  0.1420,  0.1521,  0.1568,
         0.2646,  0.2656,  0.3157,  0.3220,  0.3461,  0.3984,  0.4190,  0.5443,
         0.5579,  0.5913,  0.6148,  0.6469,  0.6469,  0.6523,  0.6674,  0.7059,
         0.7141,  0.7822,  0.8154,  0.8668,  0.9291,  0.9804,  0.9853,  0.9941,
         1.0376,  1.0393,  1.0697,  1.1024,  1.1126,  1.1532,  1.2289,  1.3403,
         1.3494,  1.4279,  1.4994,  1.5031,  1.5437,  1.6789,  2.0832,  2.2444,
         2.3935,  2.6056,  2.6057,  2.6632])
torch.manual_seed(43052)
net = torch.nn.Linear(in_features=1,out_features=1) 
net(_x)
RuntimeError: mat1 and mat2 shapes cannot be multiplied (1x100 and 1x1)

잘못된사용2

torch.manual_seed(43052)
net = torch.nn.Linear(in_features=2,out_features=1) # bias=False를 깜빡..
net.weight
Parameter containing:
tensor([[-0.2451, -0.5989]], requires_grad=True)
net.bias
Parameter containing:
tensor([0.2549], requires_grad=True)
plt.plot(x,y,'o')
plt.plot(x,net(X).data,'--')
plt.plot(x,X@torch.tensor([[-0.2451],[-0.5989]])+0.2549,'-.')

  • 수식표현: \(\hat{\bf y} = {\bf X} {\bf \hat W} + \hat{b}= \begin{bmatrix} 1 & x_1 \\ 1 & x_2 \\ \dots & \dots \\ 1 & x_{100} \end{bmatrix} \begin{bmatrix} -0.2451 \\ -0.5989 \end{bmatrix} + 0.2549\)

숙제

(1) 자신의 학번을 seed로 설정하고 표준정규분포에서 5개의 난수를 생성하고 순서대로 정렬한 뒤 이를 x로 저장하라. (아래코드참고)

torch.manual_seed(202043052) 
x,_ = torch.randn(5).sort()

(2) 아래와 같이 torch.nn.Linear()를 이용하여 적당한 네트워크를 생성하고 “최초의 직선” \(\hat{y}_i\)가 아래와 같이 구해지도록 net.weight 혹은 net.bias의 값을 수정하라.

\[ \hat{y}_i = 2.5 x_i - 7, \quad i=1,2,3,4,5 \]

단, \(x_1,x_2,\dots,x_5\)는 x의 원소이다.

note: 공부를 위해서 bias를 넣은 버전과 넣지 않는 버전 모두 계산해 보세요. (숙제제출은 한 방법으로만 구현해도 무방)

(풀이)

torch.manual_seed(202043052) 
x,_ = torch.randn(5).sort()
x = x.reshape(-1,1)
X = torch.concat([torch.ones(5).reshape(-1,1),x],axis=1)
x,X
(tensor([[-2.9777],
         [-0.2220],
         [-0.1181],
         [ 0.1084],
         [ 1.7688]]),
 tensor([[ 1.0000, -2.9777],
         [ 1.0000, -0.2220],
         [ 1.0000, -0.1181],
         [ 1.0000,  0.1084],
         [ 1.0000,  1.7688]]))

(ver1) bias를 넣음

net1=torch.nn.Linear(in_features=1,out_features=1,bias=True) 
net1.weight.data, net1.bias.data
(tensor([[0.0092]]), tensor([0.1899]))
net1.weight.data = torch.tensor([[2.5]])
net1.bias.data = torch.tensor([-7.0])
net1.weight.data, net1.bias.data
(tensor([[2.5000]]), tensor([-7.]))
net1(x), 2.5*x-7
(tensor([[-14.4443],
         [ -7.5551],
         [ -7.2952],
         [ -6.7290],
         [ -2.5781]], grad_fn=<AddmmBackward0>),
 tensor([[-14.4443],
         [ -7.5551],
         [ -7.2952],
         [ -6.7290],
         [ -2.5781]]))

(ver2) bias를 넣지 않음

net2=torch.nn.Linear(in_features=2,out_features=1,bias=False) 
net2.weight.data, net2.bias
(tensor([[-0.6152, -0.6372]]), None)
net2.weight.data = torch.tensor([[-7.0, 2.5]])
net2.weight.data
tensor([[-7.0000,  2.5000]])
net2(X), 2.5*x-7
(tensor([[-14.4443],
         [ -7.5551],
         [ -7.2952],
         [ -6.7290],
         [ -2.5781]], grad_fn=<MmBackward0>),
 tensor([[-14.4443],
         [ -7.5551],
         [ -7.2952],
         [ -6.7290],
         [ -2.5781]]))