Calculate t maximums in single vector

Question

Moe Joe 2016-12-3

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https://ww2.mathworks.cn/matlabcentral/answers/315203-calculate-t-maximums-in-single-vector

编辑： Stephen23 2016-12-3

I have an iterative program for linear block codes (k,n), and at some point, I add code-words base10

The addition result in a vector of size (1,n)

I need to find the maximum (t) elements in this vector without going into loops operations, as the time of program execution is very important.

Example: if my Vector is (V)=(1,n)

V=[68 61 35 37 18 80 50 36 78 24 85 82 85 38 39 87 47 58 70 97 55 64 58 93 87 17 18 25 76 20 99 71]

I want a direct command that can calculate the maximum 5 elements of the Vector (V).

Kindly help.

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Answer 1

Star Strider 2016-12-3

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在 MATLAB Online 中打开

You can always create your won function file from this code to produce your ‘direct command’:

V=[68 61 35 37 18 80 50 36 78 24 85 82 85 38 39 87 47 58 70 97 55 64 58 93 87 17 18 25 76 20 99 71];
Vs = sort(V,'descend');
Out = Vs(1:5)
Out =
    99    97    93    87    87

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Moe Joe 2016-12-3

Perfect, thanks a lot.

Star Strider 2016-12-3

My apologies for the delay. The other option would be to ask for two outputs from the sort function. The second will give you the indices of the sorted elements in the original vector.

From the documentation:

[B,I] = sort(_) also returns a collection of index vectors for any of the previous syntaxes. I is the same size as A and describes the arrangement of the elements of A into B along the sorted dimension. For example, if A is a numeric vector, B = A(I).

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Answer 2

John D'Errico 2016-12-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/315203-calculate-t-maximums-in-single-vector#answer_245785

Sort them. Then take the first 5 elements from the sort. WTP?

No. It is not ONE single command. Not an option. Of course, nothing stops you from writing a function that does exactly that, in which case it will be one line.

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Moe Joe 2016-12-3

编辑：Stephen23 2016-12-3

在 MATLAB Online 中打开

Already did this function:

% This is a function locates the positions of maximum (t) numbers in a

 function [v]=maxvic(X,t);
 vector V(1,n).
    n=length(X);
    v=zeros(1,n);       
    for i = 1:t;
        [y j]=max(X,[],2);
        v(j)=1;
        X(j)=0;
    end
    end