Kardi Teknomo's Blog

I updated the Matlab code for distance matrix computation. Now it can handle multidimensional variables.  Here is the new code:

function d=DistMatrix(A,B)

             %%%%%%%%%%%%%%%%%%%%%%%%%

             % DISTMATRIX return distance matrix between points in A=[x1 y1 ... w1] and in B=[x2 y2 ... w2]

             % Copyright (c) 2005-2009 by Kardi Teknomo,  http://people.revoledu.com/kardi/

             %

             % Numbers of rows (represent points) in A and B are not necessarily the same.

             % It can be use for distance-in-a-slice (Spacing) or distance-between-slice (Headway),

             %

             % A and B must contain the same number of columns (represent variables of n dimensions),

             % first column is the X coordinates, second column is the Y coordinates, and so on.

             % The distance matrix is distance between points in A as rows

             % and points in B as columns.

             % example: Spacing= dist(A,A)

             % Headway = dist(A,B), with hA ~= hB or hA=hB

             %          A=[1 2 3; 4 5 6; 2 4 6; 1 2 3]; B=[4 5 1; 6 2 0]

             %          dist(A,B)= [ 4.69   5.83;

             %                       5.00   7.00;

             %                       5.48   7.48;

             %                       4.69   5.83]

             %

             %          dist(B,A)= [ 4.69   5.00     5.48    4.69;

             %                       5.83   7.00     7.48    5.83]

             %%%%%%%%%%%%%%%%%%%%%%%%%%%

             [hA,wA]=size(A);

             [hB,wB]=size(B);

             if wA ~= wB,  error(’ second dimension of A and B must be the same’); end

             for k=1:wA

                  C{k}= repmat(A(:,k),1,hB);

                  D{k}= repmat(B(:,k),1,hA);

             end

             S=zeros(hA,hB);

             for k=1:wA

                  S=S+(C{k}-D{k}’).^2;

             end

             d=sqrt(S);

For historical purposes, I posted here the previous code that work only for 2 dimensions:

function d=dist(A,B)

% DIST return distance matrix between point A=[x1 y1] and B=[x2 y2]

% Number of points in A and B are not necessarily the same.

% It can be use for distance-in-a-slice, distance-between-slice,

% and distance between guest-points-and-the-points

% A and B must contain two columns,

% first column is the X coordinates

% second column is the Y coordinates

% The distance matrix are distance between points in A as row

% and points in B as column.

% example: distance-in-a-slice= dist(A,A)

% distance between guest-point-and-the-point = dist(A,B) , hA=hB

% distance between slices = dist(A,B), with hA ~= hB or hA=hB

% A=[1 2; 3 4; 5 6]; B=[4 5; 6 2; 1 5; 5 8]

% dist(A,B)= [ 4.24 5.00 3.00 7.21;

% 1.41 3.61 2.24 4.47;

% 1.41 4.12 4.12 2.00 ]

[hA,wA]=size(A)

[hB,wB]=size(B)

if hA==1& hB==1 

d=sqrt(dot((A-B),(A-B)));

else

C=[ones(1,hB);zeros(1,hB)]

D=flipud(C)

E=[ones(1,hA);zeros(1,hA)]

F=flipud(E)

G=A*C % = repmat(A(:,1),1,hB)

H=A*D % = repmat(A(:,2),1,hB)

I=B*E % = repmat(B(:,1),1,hA)

J=B*F % = repmat(B(:,2),1,hA)

d=sqrt((G-I’).^2+(H-J’).^2)

end