How to find a matrix inside a larger matrix?

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Jose Grimaldo 2020-4-28

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回答： SaiDileep Kola 2020-5-8

Im trying to find a smaller matrix inside a larger matrix using explicit loops. I know there is functions and probably easier to locate if there is matching matrix inside a larger matrix. I want to locate matrix M, inside matrix A. How can i set up the for loops since both matrix are different size?

A,6x6 matrix

A=[8 2 9 7 6 7;

9 5 4 1 7 0;

1 9 8 6 7 2;

5 4 1 0 3 0;

9 8 6 8 6 0;

4 1 0 5 4 1];

B, 3x3 matrix

M=[5 4 1; 9 8 6; 4 1 0];

[r,c]=size(A)

[row,col]=size(M)

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jessupj 2020-4-28

编辑：jessupj 2020-4-28

在 MATLAB Online 中打开

if you're beholden to using loops:

you can iterate only a portion of the rows, columnns that fit inside the larger matrix, and test whether the submatrix starting at the appropriate row,col (ie. upper left index) matches the desired matrix. if it matches, store the row,col

match_ul=[]
for rr = 1:(r-row+1)
    for cc = 1:(c-col+1);        
       if isequal( A( rr:(rr+row-1), cc:(cc+col-1) ), M  );
          match_ul = [match_ul; [rr cc] ]; 
       end
    end
end

then you can iterate over the rows of this list to test:

k=1
A( match_ul(k,1)+(0:row-1), match_ul(k,2)+(0:col-1))
ans =
     5     4     1
     9     8     6
     4     1     0
k=2
A( match_ul(k,1)+(0:row-1), match_ul(k,2)+(0:col-1))
ans =
     5     4     1
     9     8     6
     4     1     0