MATLAB: Looped vector calculation and storage of answer

for looploopmatrixvector

Hello, I have two horizontal vectors which contain points for plotting a circle; vector "x" for x-coordinates and vector "y" for y-coordinates. I am trying to write a piece of code which will determine the largest chord within that circle. The approach I am taking is to use the distance formula (sqrt((x2-x1)^2)+((y2-y1)^2)) and calculate the distance between the first point and the rest – store all the distances. Then the distance between the second point and the rest – store all distance to same place. And continue this till the last point. In the end I shall have a vector (or matrix) which contains all these distances, I can then run a "max" command to find the maximum distance. I am just not sure how to implement this into MatLab, in a neat looped script. All and any help will be greatly appreciated.

Best Answer

You can use my interdists() function below. Since you say it is a circle, I don't see why you would want to compare all pairs of points. The only way this can give you a good approximation of the diameter is if the circle is well-sampled, and in that case, the distance to one particular point ,e.g.,
 data=[x;y];
 distances = interdists(data(:,1),data);
ought to be enough.
function Graph=interdists(A,B)
%Finds the matrix of distances between point coordinates
%




% (1) Graph=interdists(A,B)
%
% in:
% 




% A:  matrix whose columns are coordinates of points, for example 
%          [[x1;y1;z1], [x2;y2;z2] ,..., [xM;yM;zM]]
%     but the columns may be points in a space of any dimension, not just 3D.
% 
% B:  A second matrix whose columns are coordinates of points in the same
%     Euclidean space. Default B=A.
% 
% 
% out:
% 
% Graph: The MxN  matrix of separation distances in l2 norm between the coordinates. 
%        Namely, Graph(i,j) will be the distance between A(:,i) and B(:,j).
%
%
% (2) interdists(A,'noself') is the same as interdists(A), except the output 
%     diagonals will be NaN instead of zero. Hence, for example, operations
%     like min(interdists(A,'noself')) will ignore self-distances.
%
% See also getgraph
noself=false;
if nargin<2  
    B=A; 
elseif ischar(B)&&strcmpi(B,'noself')
    noself=true;
    B=A;
end
N=size(A,1);
B=reshape(B,N,1,[]);
Graph=l2norm(bsxfun(@minus, A, B),1);
Graph=squeeze(Graph);
if noself
    n=length(Graph);
   Graph(linspace(1,n^2,n))=nan;
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