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Math Help - Pre-Mulpilication Question

  1. #1
    Newbie richard_c's Avatar
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    Pre-Mulpilication Question

    I need help with these two questions....

    I need to discuss what is meant by 'pre-multiplication' in Matrix Analysis. Anyone any ideas/websites?

    ...and also, I ned to explain why commutative law doesnt work for matricies.

    Ive looked on the web for answers, but failed to come accross anything!

    can somebody please help?

    Thanks
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  2. #2
    Junior Member
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    Melbourne
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    Quote Originally Posted by richard_c View Post
    I need help with these two questions....

    I need to discuss what is meant by 'pre-multiplication' in Matrix Analysis. Anyone any ideas/websites?

    ...and also, I ned to explain why commutative law doesnt work for matricies.

    Ive looked on the web for answers, but failed to come accross anything!

    can somebody please help?

    Thanks
    Cummuative law states that a x b = ab and b x a =ab ... this doesnt apply for matrixes...

    because its row by column system... if i was to prove this.. i would simply do a [[a,b][c,d]]x[[e,f][g,h]] then do [[e,f][g,h]]x [[a,b][c,d]] show they are not the same

    Premultiplication is when you try and get rid of the matrix on one side you times it by the inverse yes... so then you times the other side by the inverse in the same fashion e.g

    A x B = X

    A^-1xA x B = A^(-1)X

    B = A^(-1)X
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