Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I apologize in advance for how messy this is, I've never had to use latex.

\begin{matrix} 10 \\ 40 \\ 30 \\ 20 \end{matrix}

This is matrix A

\begin{matrix} 1 \\ 2\\ 3\\ 4\\ \end{matrix}

This is matrix B

\begin{matrix} 1 \\ 1\\ 1\\ 1\\ \end{matrix} This is matrix C

\begin{matrix} -9 \\ 17\\ -7\\ -1\\ \end{matrix}

This is matrix D

How does $A*4(B)*-15(C)=D$ ?

It's an example in my notes that I need to know, and for the life of me I can't figure it out. For more context:

$y_i=\alpha x_i+\beta+\epsilon_i$ for a regression chart, with matrix B being the x values and matrix A being the y values. Matrix D is the values of the $\epsilon$ values. How do we arrive at $\epsilon$?

share|improve this question
I'm afraid you'll have to read again about LaTeX adn re-wrtie your question as it is pretty unclear: product of matrices is defined iff the left one's numer of columns equals the right one's number of rows. As you wrote it it makes no sense. It also would be a good idea, imo, that you'd do something about that poor accept rate of yours. –  DonAntonio Oct 25 '12 at 3:19
Take a look at this answer –  Pragabhava Oct 25 '12 at 3:26

1 Answer 1

up vote 1 down vote accepted

What you actually seem to have is $A=4B+15C+D$ except for a transposition in $A$. Perhaps you meant $A-4B-15C=D$?

share|improve this answer
Oh that's exactly what it is! Thank you very much, it makes perfect sense too. –  Unknown Oct 25 '12 at 3:29

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.