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How to relate or understand this code with math formula?

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Mauricio Escobar
Mauricio Escobar 2013-3-12
Having a matrix (Vertices) with vertices points of a skeleton line (all points x,y). And two (column) vector matrices Na and Nb which describe the logical indexes of the matrix Vertices... can someone explain me better (the actual mathematics) of these pieces of code? Well, actually are the same:
% Correct for sampling differences
Ta = -sqrt(sum((Vertices-Vertices(Na,:)).^2,2));
Tb = sqrt(sum((Vertices-Vertices(Nb,:)).^2,2));
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Mauricio Escobar
Mauricio Escobar 2013-3-13
编辑：Mauricio Escobar 2013-3-13
So is the distance between two points: sqrt[ (x - y)^2 +(x'- y')^2 ]
I still have one doubt...
The part after squaring: ,2 ));
Inside the sum(().^2 , 2)
What does it do?
Is it to sum two columns?

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Doug Hull
Doug Hull 2013-3-12
It looks like it is taking the delta between every vertex in the list and a specific vertex (a or b).
It is then squaring those two scalars, deltaX and deltaY
It is then summing them
Then taking the square root of the is. Is is negating the first one.
Essentially, it is finding the distance between a point and a list of points.
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Walter Roberson
Walter Roberson 2013-3-13
sum along the second dimension (i.e., along the rows). sum() defaults to summing down the columns.

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