How to relate or understand this code with math formula?

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));

[Mauricio Escobar]

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?

Answer 1

[Doug Hull]

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.

[Mauricio Escobar]

Thanks Doug Hull (excellent videos on GUI BTW! Thanks for those, a lot!)

When you say delta, what do you mean? The difference, right?

[Mauricio Escobar]

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?

[Walter Roberson]

sum along the second dimension (i.e., along the rows). sum() defaults to summing down the columns.

[Mauricio Escobar]

Thanks Walter!