How do I interpret this form of sigma notation? Do e1 and e2 take on all combinations of 1 and -1? If they do, what's the point? They just get multiplied inside the sum! FYI, this comes from equation 8 in the following paper: http://personal.mecheng.adelaide.edu.au/will.robertson/research/2012-magcoil.pdf

weird notation

  • $\begingroup$ Yes, they take on $\pm 1$ values. There are 4 terms in the sum. $\endgroup$ – user147263 Dec 26 '14 at 6:20

The meaning is $$\sum_{e_1=-1,+1}\sum_{e_2=-1,+1}e_1e_2m_1...$$

Look at equation 10 underneath that, $m_1$ depends on $e_1$ and $e_2$, so the succeeding factor is not constant as $e_1$ and $e_2$ vary.

  • $\begingroup$ And the notation indicates that they vary independently over the set $\{1,-1\}$. $\endgroup$ – Brian M. Scott Dec 26 '14 at 6:21
  • $\begingroup$ Oh wow! I didn't see that. Am I right in thinking that (e1,e2) will be (1,1) then (1,-1) then (-1, 1) and finally (-1, -1)?? $\endgroup$ – Jordan Dec 26 '14 at 6:22
  • $\begingroup$ @Jordan Yes, I've added a clarification. $\endgroup$ – Suzu Hirose Dec 26 '14 at 6:27

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