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desalexus

  • 11 months ago

How can you determine whether a matrix product AB is defined?

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  1. Loser66
    • 11 months ago
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    @Mertsj explain him, please.

  2. Mertsj
    • 11 months ago
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    You're doing fine. Give an example. That will help.

  3. desalexus
    • 11 months ago
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    its HER and like this A is 2×3 and B is 3×2, so AB is (2×3)(3×2).

  4. RolyPoly
    • 11 months ago
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    \[A_{m\times n}B_{n\times p}\]? The number of columns of A = number of rows of B

  5. RolyPoly
    • 11 months ago
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    Dimension of AB would be m×p

  6. desalexus
    • 11 months ago
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    Thanks

  7. Mertsj
    • 11 months ago
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    It depends on the dimensions:

  8. mathmale
    • 11 months ago
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    The example that Desalexus presents is illustrative: A is 2×3 and B is 3×2, so AB is (2×3)(3×2). Note how Matrix A has 2 rows and 3 columns, and B 3 rows and 2 columns. We can indeed multiply matrices A and B (in that order).

  9. Mertsj
    • 11 months ago
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    |dw:1388979444164:dw|

  10. Mertsj
    • 11 months ago
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    |dw:1388979475429:dw|

  11. RolyPoly
    • 11 months ago
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    |dw:1388979474597:dw|

  12. mathmale
    • 11 months ago
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    Yes, Mertsj, and you can make that statement more precise by stating that "the number of columns of the first matrix must equal the number of rows of the second. RolyPoly is correct in his drawing (immediately above), whereas I found that I was wrong at the onset (and have deleted my incorrect statement accordingly)!

  13. mathmale
    • 11 months ago
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    I'd rather find my own mistakes than have someone else find them for me! :)

  14. Mertsj
    • 11 months ago
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    Sometimes it is easier for the asker to see an example than to decipher a bunch or words but it is good to have both so the asker can choose.

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