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Topic review (newest first)
- bob bundy
- 2012-10-18 08:50:27
Bob
- Deon588
- 2012-10-18 07:29:03
Yes that was also the next question in the exam paper I did, worked out perfectly at the end 
- bob bundy
- 2012-10-17 23:39:52
hi Deon588
I know the rule for multiplying two matrices. I dareay you could devise a rule for three but it would be hard to remember. So two at a time is simplest.
You shouldn't assume that matrices can be swopped around like numbers but associativity { (AB)C = A(BC) } does work.
Beware: commutativity doesn't. { AB ≠ BA }
Did you try my practice suggestion?
and you should find that inverse A = E3.E2.E1
This would be a good check that you have inv A right and that your multiplying is OK.
Bob
- bobbym
- 2012-10-17 22:10:27
Hi Deon588;
Always break a big problem down into smaller pieces that you know how to do. This top down design is very common in programming. You knew how to do 2 matrices.
- Deon588
- 2012-10-17 22:04:47
Hi Bob thanks a lot for all the effort. I had no idea how to multiply more than 2 matrices so I tried doing all 3 at once...
- bob bundy
- 2012-10-17 04:12:02
and you should find that inverse A = E3.E2.E1
This would be a good check that you have inv A right and that your multiplying is OK.
Bob
- bob bundy
- 2012-10-17 04:04:49
hi Deon588
Your inverses are correct, so then you need to do the multiplying.
(AB)C = A(BC) for matrices so you have a choice of which pair you multiply first. But you must preserve order.
eg if AB = D you then do DC not CD.
I'm going to do these both ways in case I choose the way you didn't (if you see what mean)
or
Bob
- zetafunc.
- 2012-10-17 03:30:11
Never mind, bobbym was faster.
- zetafunc.
- 2012-10-17 03:29:47
You multiplied the matrices incorrectly
- bobbym
- 2012-10-17 03:28:19
Hi;
Your mistake is in line 3. Check how you multiplied those matrices.
- Deon588
- 2012-10-17 03:17:36
Hi Bobbym any idea where I made a mistake?
Thanks a lot
- bobbym
- 2012-10-17 00:32:17
Hi;
I am getting:
which can be inverted.
- Deon588
- 2012-10-17 00:17:54
Hi all. I think i'm making a mistake somewhere as the matrix I get after multiplying doesn't seem to be invertible and the next question is to find A^-1. Is this the right way to do this?
Thanks in advance