comparing between two arrays

Question

mariam 2013-10-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/89300-comparing-between-two-arrays

评论： mariam 2013-10-9

sorry if my question is trivial , but i'm still beginner and need your help. i have 3 points in the space say a , b, c each one is an array 2x3 , say a=[2 3 4 ; 9 8 7] ,b =[ 5 2 1 ; 6 3 2] , c=[ 4 7 1; 1 2 3]. i want to compare the distance between points a and b (dist12) with the distance between a and c (dist13), which is longer? thank you

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Jan 2013-10-7

@mariam: No, it is not clear enough. "Distance" is defined for single points only. Therefore it is not uniquely defined, what you are looking for.

mariam 2013-10-8

ok , i will explain with more details , i work in clustering using particle swarm . for example i have 3 particles each one has 2 cluster (this is why each array has two rows). a is particle 1 , b is particle 2 , particle 3 is c . particle 1 (a) is the best solution. so i want to compute the max distance of the particles (b , c ) from particle (a). l know how to compute the euclidean distance from each array to (a). for example distance ab =[ 4.3589 ; 11] and distance ac = [ 5.3852 ;3]. i want to compute max distance .

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Answer 1

David Sanchez 2013-10-7

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https://ww2.mathworks.cn/matlabcentral/answers/89300-comparing-between-two-arrays#answer_98820

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   a=[2 3 4 ; 9 8 7];
   b =[ 5 2 1 ; 6 3 2];
   c=[ 4 7 1; 1 2 3];
dist_ab_cluster_1 = norm(b(1,:)-a(1,:));
dist_ab_cluster_2 = norm(b(2,:)-a(2,:));
dist_ac_cluster_1 = norm(c(1,:)-a(1,:));
dist_ac_cluster_2 = norm(c(2,:)-a(2,:));
dist_ab_cluster_1 =
      4.3589
dist_ab_cluster_2 =
      7.6811
dist_ac_cluster_1 =
      5.3852
dist_ac_cluster_2 =
     10.7703

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mariam 2013-10-7

thank you very much , but if i want to treat the particle which contains two cluster as one unit ....i mean to compare between the array p1= [4.3589 ; 7.6811] and p2=[5.3852 ;10.7703] to know which distance is longer . thank you

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Answer 2

Andrei Bobrov 2013-10-7

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/89300-comparing-between-two-arrays#answer_98836

在 MATLAB Online 中打开

   a=[2 3 4 ; 9 8 7]; b =[ 5 2 1 ; 6 3 2]; c=[ 4 7 1; 1 2 3];
   data = cat(3,a,b,c);
   s = size(data);
   t = reshape(data(:,:,nchoosek(1:s(3),2)')  , s(1),s(2),2,[]);
   out = squezze(sqrt(sum(diff(t,[],3).^2,2)));