If only one positive elem per row (rest are 0), then fill both sides of positive element

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Dave
Dave 2015-2-20
编辑： John D'Errico 2015-2-20
Hi, I have a square matrix of non-negative elements. In each row, at least one element is positive.
For rows where there is only one positive element (the rest are 0) I need to put 1e-4 next to that element, both sides. In A below, the second and last row have only 1 positive (note last row has only one side to add)
A=...
[0.9 0.1 0 0;
0 0.8 0 0;
0 0.1 0.7 0.1;
0 0 0 0.9]
Ouput should be:
B=...
[0.9 0.1 0 0;
1E-4 0.8 1E-4 0;
0 0.1 0.7 0.1;
0 0 1E-4 0.9]
The dimension of the matrix is fixed, so I can get rows that need to be changed (if result is 3 in this case) with
sum(A==0,2)
But this doesn't tell me the position of the positive element (I could use something like find(A) ) , nor fill both sides (loop free if possible)

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采纳的回答

Guillaume
Guillaume 2015-2-20
A = [0.9 0.1 0 0
0 0.8 0 0
0 0.1 0.7 0.1
0 0 0 0.9];
Apadded = [zeros(size(A, 1), 1) A zeros(size(A, 1), 1)]; %pad to avoid dealing with edges
lonelyrows = find(sum(A ~= 0, 2) == 1);
[~, singlecols] = find(Apadded(lonelyrows, :));
Apadded(sub2ind(size(Apadded), [lonelyrows lonelyrows], [singlecols-1 singlecols+1])) = 1e-4;
Afilled = Apadded(:, 2:end-1)

更多回答（2 个）

Sean de Wolski
Sean de Wolski 2015-2-20
编辑：Sean de Wolski 2015-2-20
And just for fun:
A=...
[0.9 0.1 0 0;
0 0.8 0 0;
0 0.1 0.7 0.1;
0 0 0 0.9];
B = A;
sgn = sign(A)==1;
B(logical(conv2(double(bsxfun(@and,sum(sgn,2)==1,sgn)),[1 0 1],'same'))) = 1e-4
dpb
dpb 2015-2-20
Find the locations needing to be worked around. Pick one dimension first as you've done; I'll stick with the rows...
>> irow=find(sum(A>0,2)==1)
irow =
2
4
>> [~,icol]=ind2sub(size(A(irow,:)),find(A(irow,:)>0))
icol =
2
4
>>
These are now indices in the original array since didn't reduce the number of columns by subselecting the rows.

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