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Either my brain is seriously fried up right now or the computer is wrong.

If I have a matrix $\begin{bmatrix} 4 & -2\\ 2 & -1 \\ 0 & 0 \end{bmatrix}$ multiply by its transpose $\begin{bmatrix} 4 &2 &0 \\ -2&-1 &0 \end{bmatrix}$, I should get a $3 \times 3$ $\begin{bmatrix} 20 &10 &0 \\ 10 &5 &0 \\ 0&0 &0 \end{bmatrix}$

For some reason Maple is giving me a $2 \times 2$ $\begin{bmatrix} 20 &10 \\ 10 &5 \\ \end{bmatrix}$

Why did they delete the last row and column of 0s? You can't do that

  • 2
    Note, though, that if you multiplied them the other way, you should have gotten \left(\begin{array}{rr}20&-10\\-10&5\end{array}\right)and not what you say you got.2012-04-10

2 Answers 2

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You have multiplied the second matrix with the first matrix. Sice matrix multiplication is not commute the answer is wrong. And you have also ignored the negative signs. They should not be ignored.

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Do you try the result with one row of os or try some square matrix with one row of os?

Maybe is the storage of maple?