1
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Time to debug exercise number nine.

2
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So we want to produce a lower triangular matrix from this predefine to the array and now a lower triangular

3
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matrix is one where everything above the main diagonal is zero.

4
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In this case, the values that indices zero one zero two and one two should be zero.

5
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But if we run the current code, what are we going to get, let's see.

6
00:00:28,110 --> 00:00:29,790
OK, Lisa didn't crash.

7
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I'm going to have the usual breakpoint so I can at least visualize what the heck is happening here.

8
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Launched the debugger.

9
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We're at the first pass I zero is zero, nothing should happen when I injera zero, but this condition

10
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is going to evaluate to true.

11
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Sending this to.

12
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So we'll take off the equal sign and try again.

13
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OK, but now nothing happens in the first pass.

14
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Or the second pass, which means whoever wrote this code did not know what they were doing.

15
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OK, so I'm going to remove this code entirely because sometimes it's better to just start over than

16
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to fix something that's completely broken.

17
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OK, relaunched the debugger.

18
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Starting again, I zero G is zero here, we don't want to do anything.

19
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But now the inner loop suddenly breaks.

20
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Hmm, now I is one.

21
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Wait a second.

22
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I need to update indices 01 and 02, but the way the inner loop code was designed, it's never going

23
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to reach them.

24
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It seems like they tried to get all fancy, but in reality, we need to loop through every single element

25
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in each row so we can use a regular nested loop.

26
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I don't know what the heck they were doing.

27
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Relaunched the debuggers starting again.

28
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I zero g zero.

29
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Here, we don't want to do anything, but when I zero in just one.

30
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Now we want to set this to zero.

31
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OK, I think I found the pattern we should only set the element equal to zero if its index is higher

32
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than the row index I.

33
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So if Jay is higher than I.

34
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Then we're going to set that element equal to zero.

35
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OK, try it out now.

36
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Here, the condition is false.

37
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But now Jay is bigger than I said, the element equal to zero.

38
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Once more here.

39
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In the second pass, I equals one, this condition is going to be false for the first two elements in

40
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that row, but then it's going to be true for inducts to.

41
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And for the final row, the condition should be false through about.