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#2 2012-10-17 00:32:17
- bobbym
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Re: Product of elementary matrices
Hi;
I am getting:
which can be inverted.
In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.
#4 2012-10-17 03:28:19
- bobbym
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Re: Product of elementary matrices
Hi;
Your mistake is in line 3. Check how you multiplied those matrices.
In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.
#7 2012-10-17 04:04:49
- bob bundy
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Re: Product of elementary matrices
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
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
#8 2012-10-17 04:12:02
- bob bundy
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Re: Product of elementary matrices
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
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
#10 2012-10-17 22:10:27
- bobbym
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Re: Product of elementary matrices
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.
In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.
#11 2012-10-17 23:39:52
- bob bundy
- Moderator
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Re: Product of elementary matrices
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
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
