Maxk gives an incorrect result

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Kk 2022-4-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1702600-maxk-gives-an-incorrect-result

评论： Voss 2022-4-23

采纳的回答： Voss

在 MATLAB Online 中打开

Hi all,

I am trying to get 4 different value from a matrix. I am using maxk to find these values indices. Maxk can find first two maximum value with indices but when I try to find third it gives an incorrect result. for example when ı select row "1" it found 2 maximum value with their column in matrix and gives me 7-15 then I select 7 for my row it should needs to give me 8th column but it gives 1. I cannot understand why

Here is my code:

for i = nodes
    if i == 1 [~,seed] = maxk(m(1:n),2);
    end
end
s1 = seed(1,1);
s2 = seed(1,2);
for i = nodes
    if i == 7 [~,seed2] = maxk(m(7,n),1);
    end
end

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采纳的回答

Voss 2022-4-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1702600-maxk-gives-an-incorrect-result#answer_948400

在 MATLAB Online 中打开

For the case that i == 1 you have:

maxk(m(1:n),2)

m(1:n)is the first n elements of m (going in column-major order, which is what MATLAB uses). For example:

m = magic(4)
m = 4×4
    16     2     3    13
     5    11    10     8
     9     7     6    12
     4    14    15     1
n = 6;
m(1:n)
ans = 1×6
    16     5     9     4     2    11

For the case that i == 7, you have:

maxk(m(7,n),2)

m(7,n) is the element(s) of m at row 7, column(s) n. If n is a scalar, that's one element. For example:

m = magic(7)
m = 7×7
    30    39    48     1    10    19    28
    38    47     7     9    18    27    29
    46     6     8    17    26    35    37
     5    14    16    25    34    36    45
    13    15    24    33    42    44     4
    21    23    32    41    43     3    12
    22    31    40    49     2    11    20
n = 6;
m(7,n)
ans = 11

If you want to use maxk on rows of m, then the syntax would be:

maxk(m(1,:),2) % using first row of m
maxk(m(7,:),2) % using 7th row of m

For example (using m as the 7x7 magic square still):

m(1,:)
ans = 1×7
    30    39    48     1    10    19    28
m(7,:)
ans = 1×7
    22    31    40    49     2    11    20
[~,seed] = maxk(m(1,:),2)
seed = 1×2
     3     2
[~,seed2] = maxk(m(7,:),2)
seed2 = 1×2
     4     3