Possibility to know the index of the max() value

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André Pacheco
André Pacheco 2012-12-31
Hello there,
I have a problem where I need to keep the maximum value and its position. In a while cycle I have one matrix that is created randomly, and I have to keep the maximum sum of the row in each iteration.
For example, I have one matrix (3 rows by 4 columns) that is p.e matrix a =
4 5 6 2
8 5 7 1
2 3 5 2
And another matrix that is (3 by 1) that keeps the sum of the matrix in some iteration p.e. matrix C=
17
21
12
Then I have a vector that keeps the max of the matrix C in order to build a graph of the evolution of the maximum value.
aux_vector=max(C);
I would like to keep the line that corresponds to the max of C, in this case the second line of the matrix a.
Thanks in advance.

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采纳的回答

Walter Roberson
Walter Roberson 2012-12-31
[aux_vector, aux_index] = max(C):
max_a = a(aux_index, :);
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Walter Roberson
Walter Roberson 2012-12-31
[aux_vector(iteration), aux_index] = max(C):
max_a(iteration,:) = a(aux_index, :);

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更多回答（1 个）

Image Analyst
Image Analyst 2012-12-31
Try this code:
sumOfRows = sum(a, 2) % Your "C"
[maxValue, rowWithTheMax] = max(sumOfRows)
Here it is in a demo where we generate lots of random matrices "a" in a loop:
format compact;
numberOfRuns = 5;
% Initialize a matrix to keep track of the rows having
% the max sum at each iteration.
maxRows = zeros(numberOfRuns, 4); % One row for each run.
for k = 1 : 5
% Generate a matrix
if k == 1
% For the first run, use
% the example matrix the poster supplied.
a = [...
4 5 6 2
8 5 7 1
2 3 5 2]
else
% Subsequent runs use a random matrix.
a = randi(9, [3 4])
end
sumOfRows = sum(a, 2) % Your "C"
[maxValue, rowWithTheMax] = max(sumOfRows)
% Store this row in an array that depends on the run.
% In other words, store the 4 values from that row of "a".
maxRows(k, :) = a(rowWithTheMax, :)
end
Hopefully it's commented well enough to explain what's going on.
  2 个评论
Image Analyst
Image Analyst 2012-12-31
Actually I noticed that this is virtually the same as Walter's. I didn't realize at first because I didn't see sum() in his code.
André Pacheco
André Pacheco 2013-1-2
I've tried and it worked! Although i used the first answers but it is the same as u made. Thanks !

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