MATLAB pdist function

Question

I am using the pdist command to find the distance between x and y coordinates stored in a matrix.

X = [100 100;
      0  100;
     100  0;
     500 400;
     300 600;];

D = pdist(X,'euclidean')

Which returns a 15 element vector. :

[0.734979755525412 3.40039811339820 2.93175207511321   1.83879677592575 2.40127440268306 2.75251513299386 2.21488402640753 1.10610649500317 1.81674017301699 0.903207751535635 1.99116952754924 1.05069952386082 1.24122819418333 1.08583377275532 1.38729428638035]

Is there a way to associate these distances with the coordinates they were derived from, i.e. store them in a matrix with the general row form:

[Length xcoordinate1 ycoordinate1 xcoordinate2 ycoordinate2]

Where there is a row for each length found?

Thanks in advance

Answer 1

MATLAB has an inbuilt command called "squareform" that converts a pdist output to an n x n distance matrix http://www.kxcad.net/cae_MATLAB/toolbox/stats/pdist.html

%# define X, D
X = [100 100;
      0  100;
      100  0;
     500 400;
     300 600;];

D = squareform(pdist(X,'euclidean'));

Answer 2

%# define X, D
X = [100 100;
      0  100;
     100  0;
     500 400;
     300 600;];

D = pdist(X,'euclidean');

%# find the indices corresponding to each distance
tmp = ones(size(X,1));
tmp = tril(tmp,-1); %# creates a matrix that has 1's below the diagonal

%# get the indices of the 1's
[rowIdx,colIdx ] = find(tmp);

%# create the output
out = [D',X(rowIdx,:),X(colIdx,:)];