Matrices: Multiplication.

Spintwo · 2003-11-29T17:57:58

I'm learning about matrix multiplication as follows. To multiply matrices, the number of columns (the up and down things) in the first matrix need to be equal to the number of rows (the left and right things) in the second matrix. Is this true? If this is true, doesn't this mean that the first matrix always has to be "smaller" (dimension wise) than the second one? (2x2 matrix)x(2x3 matrix) is possible. (3x2 matrix)x(2x3 matrix) is not possible? EDIT: Also, the above (2nd) example means that matrix multiplication is not commutative. But I read that matrix multiplication is associative. How is this possbile? Charles Hwang -aka Tazel [MonkeyHumor My Site|E-mail|NeXe|NeHe|SDL] [Google|Dev-C++|GDArticles|C++.com|MSDN] [edited by - charles hwang on November 29, 2003 4:27:56 PM]

Math and Physics Programming

Started by Spintwo November 29, 2003 03:26 PM

11 comments, last by Spintwo 20 years, 5 months ago

Spintwo

358

Author

November 29, 2003 05:30 PM

Hmm...ok with this:

[2 5] x [3 1 -4]
[2 0 1]

[2x3+2x5 2x1+5x0 2x-4+5x1]
Which equals
[16 2 -3]

Correct?

Spintwo

358

Author

November 29, 2003 05:42 PM

This is kinda of an extreme here but so, according to everything in this thread, the following matrix multiplication is possible?

(Assume x,y,z and a,b,c,d,e,f are all different real numbers)

[x y z]   [x y z]    [x y z]     [a b c d e f][x y z]  x  [a b c d e f][x y z]     [a b c d e f][x y z]     [x y z]7x3              3x6  |___are equal__|

And the resulting matrix would be a 7x6 matrix?

Kentaro

122

November 29, 2003 05:57 PM

Yep. The multiplication is possible and the result is a 7x6 matrix. Matrix multiplication is pretty easy once you''ve got the definitions in your head. =)

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Matrices: Multiplication.

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Matrices: Multiplication.

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