# Linear Algebra

1. pass

2. pass

3. yes,pass

4. first dimension:2

5. first dimension

6. not match!


A = torch.arange(20, dtype = torch.float32).reshape(5, 4)

A / A.sum(axis=1)



RuntimeError: The size of tensor a (4) must match the size of tensor b (5) at non-singleton dimension 1

It will be fine.


B = torch.arange(25, dtype = torch.float32).reshape(5, 5)

B / B.sum(axis=1)



tensor([[0.0000, 0.0286, 0.0333, 0.0353, 0.0364],

    [0.5000, 0.1714, 0.1167, 0.0941, 0.0818],

[1.0000, 0.3143, 0.2000, 0.1529, 0.1273],

[1.5000, 0.4571, 0.2833, 0.2118, 0.1727],

[2.0000, 0.6000, 0.3667, 0.2706, 0.2182]])


1. Walk:Manhattan’s distance.the â„“1 norm

# distances of avenues and streets

dist_ave = 30.0

dist_str = 40.0

dis_2pt = torch.tensor([dist_ave, dist_str])

torch.abs(dis_2pt).sum()



Can. Fly straightly and diagonally.the â„“2 norm


torch.norm(dis_2pt)



tensor(50.)

1. The shape is just the shape of the original tensor that deleted the axis required.

X.sum(axis = 0).size() torch.Size([3, 4])

X.sum(axis = 1).size() torch.Size([2, 4])

X.sum(axis = 2).size() torch.Size([2, 3])

1. $|\mathbf{x}|{2}=\sqrt{\sum{i=1}^{n} x_{i}^{2}}$

Y= torch.arange(24,dtype = torch.float32).reshape(2, 3, 4)

torch.norm(Y)



tensor(65.7571)


i = 0

for j in range(24):

i += j**2

j += 1

import math

print(math.sqrt(i))



65.75712889109438

The numbers are same.

For more:

http://d2l.ai/chapter_preliminaries/linear-algebra.html#equation-chapter-preliminaries-linear-algebra-0

The matrix should be indexed via nm instead of mn, since the original matrix is mn and this is the transposed version.

Hi @manuel-arno-korfmann, could you specify which is “the matrix” you were referred to ?

Hey @goldpiggy, the link given includes a # query parameter which directly links to “the matrix”. Does that work for you?

Hi @manuel-arno-korfmann, you mean the matirx index like $a_12$ and $a_21$? The indexes’ location is flipped, while they have to keep the original values. Ultimately, $a_mn$ and $a_nm$ have different values at the original matrix

@manuel-arno-korfmann
I think @goldpiggy is right.
A_mn:

AT_nm: