How can I find the location of the minimum and maximum

조회 수: 38(최근 30일)
Tony Montgomery
Tony Montgomery 2014년 10월 31일
댓글: Matt Tearle 2014년 10월 31일
I am to test some ill condition matrices, so I want create a loop that creates 5 random nxn matrices. Then I want to be able to find the matrix with the minimum condition number, and the one with the maximum condition number. I have the following code:
for i=1:5
Ai = rand(n,n);
C(i) = cond(Ai);
end
max(C)
min(C)
So I was able to find the min and max values, but I want to know which matrix they are associated with. If i knew where they occurred I can figure it out, but how can I find WHERE the min and max occured??

답변(3개)

SK
SK 2014년 10월 31일
편집: SK 2014년 10월 31일
[maxvalue, index_of_max] = max(C);
[minvalue, index_of_min] = min(C);

Orion
Orion 2014년 10월 31일
편집: Orion 2014년 10월 31일
Hi,
just use the second output argument of the min and max functions.
n=10;
for i=1:5
Ai = rand(n,n);
C(i) = cond(Ai);
end
[MaxVal,MaxIndex] = max(C);
[MinVal,MinIndex] = min(C);
% check
disp([C(MaxIndex),MaxVal])
disp([C(MinIndex),MinVal])

Matt Tearle
Matt Tearle 2014년 10월 31일
Others have explained how to get the index of the max or min, but I'm wondering if you actually want to know what the matrix is that it's associated with. Currently you overwrite your matrix each time through the loop, so there's no way to retrieve it. So
Ai = rand(n,n,5);
C = zeros(5,1);
for i = 1:5
C(i) = cond(Ai(:,:,i));
end
[idx,maxC] = max(C);
maxA = Ai(:,:,idx);
  댓글 수: 2
Matt Tearle
Matt Tearle 2014년 10월 31일
That's what my code does -- it keeps all the matrices in a 3-D array (n-by-n-by-5). Then once you have idx -- the index of the maximum -- you can index into Ai to get the idx element: maxA = Ai(:,:,idx);

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