a b c d
a 0/3 1/3 0/3 1/3
b 1/4 0/4 1/4 1/4
c 0/1 1/1 0/1 0/1
d 1/3 1/3 1/3 0/3
To find the importance matrix for the given internet with four websites (a, b, c, and d), we need to determine the importance of each website in terms of the number of other websites that link to it.
Here is the importance matrix for the given internet:
```
a b c d
a 0/3 1/3 0/3 1/3
b 1/4 0/4 1/4 1/4
c 0/1 1/1 0/1 0/1
d 1/3 1/3 1/3 0/3
```
1. Website a has 3 outgoing links (b, d), and out of those 3 websites, 1 links back to a (b), so the importance of a is 1/3.
2. Website b has 4 outgoing links (a, c, d), and none of those 4 websites link back to b, so the importance of b is 0/4.
3. Website c has 1 outgoing link (b), and out of that 1 website, 1 links back to c (b), so the importance of c is 1/1.
4. Website d has 3 outgoing links (a, b, c), and out of those 3 websites, 1 links back to d (b), so the importance of d is 1/3.
Please note that the importance matrix represents the fraction of incoming links to each website compared to the total number of outgoing links from the linking website.