How would I write a function that finds the closest point from a list of coordinates?

I have to write a function that calculates the distance between multiple points and a base site, then finds the closest point to the base site. This is the format I have to follow:

function [chosen_site, d] = select_closest_site( current_site, site_list, x, y )

where x and y are vectors containing the appropriate coordinates for each point, site_list is a vector with the IDs of the points that will be compared, and current_site is the base site that the distances will be calculated from.

Here's an example of how the code should function:

Consider the list of four sites, with locations x = [3, 1, 2, 2] and y = [5, 2, 4, 6]. Given current_site = 4 and site_list = [1, 3], the function should consider which of sites 1 and 3 is closer to site 4, then select site 1 as it is closer. The function should also report the distance to that site, √2:

I also have to call a function that calculates distance which I have already written. This is what I have for that:

function d = compute_distances( x_c, y_c, x, y )

d = sqrt((x_c - x).^2 + (y_c - y).^2);

end

This is what I have written so far to call in the distance function:

d = compute_distances(x(current_site), y(current_site), x, y);

How would I go about continuing past this? I assume I will have to use the min function but I'm struggling to figure out how to format it.

Any help is appreciated.

Answer 1

[Riccardo Scorretti]

Hi Joshua, you can try this:

x = [3, 1, 2, 2];
y = [5, 2, 4, 6];
current_site = 4;
site_list = [1, 3];
[chosen_site, d] = select_closest_site( current_site, site_list, x, y)

chosen_site = 1

d = 1.4142

function [chosen_site, d] = select_closest_site( current_site, site_list, x, y)
xc = x(current_site);
yc = y(current_site);
[d, ind] = min(sqrt((xc-x(site_list)).^2 + (yc-y(site_list)).^2));
chosen_site = site_list(ind);
end

[Riccardo Scorretti]

The key is that min returns two outputs. Matlab manual reads:

[M,I] = min(X) also returns the indices corresponding to the minimum values. The values in I index into the dimension of X that is being operated on. If X contains more than one element with the minimum value, then the index of the first one is returned.

[Joshua Rigby]

Thank you! This has really clarified it for me.