Newbie: Euclidean distance of a matrix??

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Usman Ali
Usman Ali 2012-4-23
hello all, i am new to use matlab so guys i need ur help in this regards. if i have a mxn matrix e.g
X=[5 3 1; 2 5 6; 1 3 2]
i would like to compute the distance matrix for this given matrix as
D= [d11 d12 d13; d21 d22 d23; d31 d32 d33]
where d(ij)= euclidean distance between row i and j.
in my thinking i applied a for loop like this
% for r=1:rows
% for c=1:cols
% for k=1:3
% d(r,c)= sqrt(sum(a(r,k)-a(c,k)).^2);
% end
% end
% end
but this thing doen't gives the desired result. can some one please correct me and also it would b nice if it would be not only for 3x3 matrix but for any mxn matrix..
thanks alot in advance i wish a nice smilling day

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采纳的回答

Sean de Wolski
Sean de Wolski 2012-4-23
Following your rules:
X=[5 3 1; 2 5 6; 1 3 2]; %sample matrix
myEdist = squeeze(sqrt(sum(bsxfun(@minus,X,reshape(X',1,size(X,2),size(X,1))).^2,2))) %Engine
Take the difference of elements in each combination of rows. Square it, sum it, root it, and squeeze it!.
  1 个评论
Usman Ali
Usman Ali 2012-4-25
that works absolutly perfect. but i have another matrix of size 10x6, applied your code and found that the ans came out to be squared root of the original Ans to be expected.
so i changed a little bit of ur code by removing sqrt(). or by squaring myEdist and then the ans was perfectly matching.
i.e
myEdist = squeeze(sum(bsxfun(@minus,X,reshape(X',1,size(X,2),size(X,1))).^2,2))
or
myEdist = squeeze(sqrt(sum(bsxfun(@minus,X,reshape(X',1,size(X,2),size(X,1))).^2,2))).^2
but when i applied the new edited code back to old 3x3 matrix. the ans was the squared of the expected ans. so i have to take again the sqrt(ans).
would it b possible to think not only for the square matrices but of any size MxN

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更多回答（1 个）

Thomas
Thomas 2012-4-23
Dunno if this is what you need:
X=[5 3 1; 2 5 6; 1 3 2]
for i=1:length(X)
dist(i,:)=pdist(X(:,i),'euclidean')';
end
dist
EDIT
All you need is
X=[5 3 1; 2 5 6; 1 3 2]
pdist(X)
or if you need a 3x3 matrix of output:
for i=1:length(X)
Y=circshift(X,i+1);
q(i,:)=pdist(Y);
q(i,i)=0;
end
q
Using Teja's comment might be the easiest:
X=[5 3 1; 2 5 6; 1 3 2]
squareform(pdist(X));
  2 个评论
Usman Ali
Usman Ali 2012-4-23
unfortunatlly thats also incorrect.
actually any distance e.g d12 could be found as
1st row minus 2nd row, square each value, add all the values in a row vector and then take the sqrt i.e
1. sum =(x(1,1)-x(2,1)).^2 + (x(1,2)-x(2,2)).^2 + (x(1,3)-x(2,3)).^2
2. d12= sqrt(sum)
so in above example the ans should be d12=d21= 6.1644
Teja Muppirala
Teja Muppirala 2012-4-23
X=[5 3 1; 2 5 6; 1 3 2]
squareform(pdist(X))
will convert it into the 3x3 matrix

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