Simviation Forum - Matrixes/Matrices

Oct 6^th, 2003 at 7:55pm

Scorpiоn Offline
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No, this has nothing to do with the movie. How do you multiply matrices? The saddest thing about all of this is even my book tells me to do it by calculator. Undecided

Sad, really.

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Reply #1 - Oct 6^th, 2003 at 9:04pm

Iroquois Offline
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Ok, let me just whip out my text. You probably won't understand a word I'm saying because I'm really bad at explaining things like this.

Say you have a matrix. Matrix A is 2(m)x3(n) and matrix B is 3(m)x3(n). Now to multiply this must be true: A(mXn) * B(nXp) = C(mXp). "n" in A must be the same as "n" in B in order to multiply. In our example, this is true.

Now to find the first entry in the 2x3 matrix. Say row 1 of matrix a is {2 1 -6} and column 1 of B is {1 0 -2}. To the first entry in row 1 of matrix C (C11 we'll call it), we must multiply then add. Therefore C11= (2)(1) + (1)(0) + (-6)(-2) = 14
Now we want to find C12 being entry two in row one. Do the same. Multiply Row 1 from A with Column 2 from B in the same fashion. Do the same for colum 3 in the to find the C13.

To find C21, 2 being the second row in C first entry in the row and column. Do the same once again. Multiply Row 2 from A with Column 1 in B in the same fashion as above. Keep doing this until you've completed all the entries.

If you still are confused, IM me with your Email and I'll send you some examples in a spread sheet. Math is something that cannot be explained through text but must be seen.

I only pretend to know what I'm talking about. Heck, that's what lawyers, car mechanics, and IT professionals do everyday. Wink

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Reply #2 - Oct 7^th, 2003 at 12:04pm

Loafing Smurf Offline
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Orendas explanation is correct. It would be easier if it was explained in plain numbers.

Scorpion, are you 16 and multiplying matrices in high school?

P.S Orenda, are you doing linear algebra? What program are you in again? I never had to multiply matrices to this point, not even high school. I just happen to know that much.

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Reply #3 - Oct 7^th, 2003 at 5:08pm

Scorpiоn Offline
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Why yes Ranger, yes I am. Roll Eyes

Righty tighty, I was gonna make a chart, but the code is spacing things weird. I'll try to do it with spacing alone.

Matrix A Matrix B

| 2| 1| 6|  | 1| 0|-2|
| 4| 9| 3|  | 1| 8| 5|
----------  |-7| 2|-7|

Matrix C

|14| ?| ?|
| ?| ?| ?|

Quote:

Multiply Row 1 from A with Column 2 from B

Wouldn't it be row 1 with row 2?

I think I get the gist of it, but I'll take you up on that spreadsheet offer anyway. Yes I do have Microsoft Excel, by the way. Wink

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Reply #4 - Oct 7^th, 2003 at 9:52pm

Iroquois Offline
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At least I'm right. We did Matrices in my 3 hour math lecture today. Tongue

I should also mention that Matrix A times Matrix B doesn't generally equal Martix B times Matrix A.

Quote:

P.S Orenda, are you doing linear algebra? What program are you in again?

They call it Calculus and Linear Algebra for Commerce. I'm in Social Sciences. I decided to focus on the Commerce related end with a minor in history. This year I'm taking:
Calculus and Linear Algebra
American History
Introduction to Management
Accounting I

Quote:

I never had to multiply matrices to this point, not even high school. I just happen to know that much.

We did matricies in Data Management in grade 12. You'll probably know it better as Finite.
BTW, what I wrote is basically a compressed version of what was in a university text. That's why it seems confusing but it really isn't.

Multiplying matricies is quite time consuming. So I won't answer Matrix C right now. I'll work on it when I get some time.

I only pretend to know what I'm talking about. Heck, that's what lawyers, car mechanics, and IT professionals do everyday. Wink

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Reply #5 - Oct 7^th, 2003 at 11:59pm

Scorpiоn Offline
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Quote:

Say row 1 of matrix a is {2 1 -6} and column 1 of B is {1 0 -2}.

Oops, OK, I reread. Wink

Now it makes perfect sense! Grin

It would be more like this:

Matrix A Matrix B

| 2| 1| 6|  | 1| 9|15|
| 4| 9| 3|  | 0| 8| 5|
----------  |-2| 2|-7|

Matrix C

|14| ?| ?|
| ?| ?| ?|

I just put question marks 'cause like you said, this takes awhile and my mom is telling me to go to bed. Thanks for the help guys! I'm sure to ace any tests now, although late as it may be, we've already had two quizzes over the stuff. Tongue

Thanks anywho! Grin

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