Summation Notation: Is \sum_{u,v} Equal to \sum_u\sum_v?

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Discussion Overview

The discussion centers on the equivalence of two summation notations, specifically whether the expression \(\sum_{u,v} H_{i-u,j-v}F_{u,v}\) is equivalent to \(\sum_u\sum_v H_{i-u,j-v}F_{u,v}\). The focus is on the notation itself rather than the specific variables involved.

Discussion Character

  • Technical explanation

Main Points Raised

  • Some participants propose that the two forms are equivalent, provided there is no confusion about the ranges of the indices.
  • Others agree, noting that the first form is often used in contexts like convolution in image processing, where it is interpreted as a double summation.
  • A participant mentions that the compact notation is used to save space, drawing a parallel to integral notation.

Areas of Agreement / Disagreement

Participants generally agree that the two summation notations are equivalent under certain conditions, specifically regarding the clarity of index ranges. However, there is no explicit consensus on all potential interpretations or contexts.

gnome
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Is

[tex]\sum_{u,v} H_{i-u,j-v}F_{u,v}[/tex]

the same as

[tex]\sum_u\sum_v H_{i-u,j-v}F_{u,v}[/tex]

?

(Don't worry about what H,F,i,j,u,v are. I'm only asking about the notation.)
 
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I only see this in the case that there could be no confusion about the range of the indicies, and so I would say yes, they are the same.
 
Yes, thanks, assuming that the ranges of the indices are unambiguous...

I read the first form in a textbook; the context is applying convolution to image data, and I don't see any way to interpret it other than as a double summation. I just wanted some reassurance that I'm not overlooking something.
 
It's written that way to save space. Similar to writing [tex]\int f \, dV[/tex] rather than [tex]\int \int \int f \, dx\, dy\, dz[/tex]
 

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