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Finding minimum value in a 2D Matrix with a region

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Vittal Rao
Vittal Rao 2015-1-26
评论： Guillaume 2015-1-26
I have a set of 18 matlab vectors(raw readings of current values) data put into a 2d matrix of B[ 18 * 16348].
I have found the indices and max value of each vector and stored in another vectors namely M( has max values of each row vector of B) and l (has indices of max of each row vector of B). [M,l]=max(B,[],2)
Now i want to find the least value of each row vector before this max value by looking backwards. This would give me the difference between max curretn and the least current before.
I wrote a loop to look backwards and check for the least value and its indices. Apparently it does not work.
Could someone help ? Below is what i am trying.
o=l;
for i=1:18
while o(i)>0
if( B(i,o(i))>B(i,o(i)-1))
o(i)=o(i)-1;
else
display(o(i));
display(B(i,o(i)));
break;
end;
break;
end;
end;

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回答（1 个）

Guillaume
Guillaume 2015-1-26
If you don't need the indices of the minimums, it's fairly straightforward using cummin:
B = [5 2 3 7 6 1 3; 3 2 1 4 8 2 0] %just for testing
[M, I] = max(B, [], 2);
cm = cummin(B, 2);
minbefore = cm(sub2ind(size(cm), [1:size(cm, 1)]', I))
diffminmax = M - minbefore
  2 个评论
Vittal Rao
Vittal Rao 2015-1-26
Thanks for that. Semms to work. But i need the indices of minima too. Any work around ?
Guillaume
Guillaume 2015-1-26
This would work with the code I've posted:
minindices = cellfun(@(row, m) find(row == m, 1), num2cell(B, 2), num2cell(minbefore))
But in that case, you might as well replace the whole lot with:
[M, I] = max(B, [], 2);
[minbefore, minindices] = cellfun(@(row, i) min(row(1:i)), num2cell(B, 2), num2cell(I))

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