How to find the index of the first absolute minimum entry of a matrix

20 visualizzazioni (ultimi 30 giorni)
I am working on a model structure optimization problem and to summarize consider this matrix:
A=[5,7,0.5,5 ; 2,0.5,4,1 ; 0.5,6,7,9]
In this matrix, 0.5 is clearly the smallest element of this matrix.
It is repeated 3 times.
Question: Can someone provide me with an algorithm that returns the index and value of this absolute minimum "only the first time it appears"
For instance:
A=[5,7,0.5,5 ; 2,0.5,4,1 ; 0.5,6,7,9];
[value,index]=somecode(A)
%returns the value of the absolute minimum
>> value = 0.5
%returns the index of the first time this absolute minimum appears
>> (3,1) % the first time it appears is in column 3 row 1 and NOT column 2 row 2
  1 Commento
Stephen23
Stephen23 il 19 Mag 2022
Your example matrix is not very good because it contains the value 0.5 in both (1,3) and (3,1) locations.
Catalytic's answer for example gives the wrong answer because of this confusion.

Accedi per commentare.

Risposta accettata

Catalytic
Catalytic il 19 Mag 2022
Modificato: Catalytic il 19 Mag 2022
A=[5,7,0.5,5 ; 2,1,4,1 ; 1,6,7,0.5],
A = 3×4
5.0000 7.0000 0.5000 5.0000 2.0000 1.0000 4.0000 1.0000 1.0000 6.0000 7.0000 0.5000
[value,index]=min(A(:))
value = 0.5000
index = 7
[Iindex,Jindex]=ind2sub(size(A),index)
Iindex = 1
Jindex = 3

Più risposte (2)

Stephen23
Stephen23 il 19 Mag 2022
A = [5,7,0.5,5;2,0.5,4,1;0.5,6,7,9];
[V,X] = min(A.',[],'all');
[C,R] = ind2sub(size(A),X)
C = 3
R = 1

Mathieu NOE
Mathieu NOE il 19 Mag 2022
hello
here you are my friend
A=[5,7,0.5,5 ; 2,0.5,4,1 ; 0.5,6,7,9]
[val,ind_linear] = min(A,[],'all','linear'); % M = MIN(X,[],'all') returns the smallest element of X.
% [M,I] = MIN(X,[],...,'linear') returns the linear indices of the
% minimum values in vector I.
ind_linear = min(ind_linear); % take only the first one in case there are multiple answers
[row,col] = ind2sub(size(A),ind_linear) % Convert from the linear index back to its row and column form.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by