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finding value of matrix in an if statement

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Sara Ismail-Sutton
Sara Ismail-Sutton 2020-11-24
编辑： Jon 2020-11-24
e issue is with line 18 of the code below. I tested it with the vector C =[1 2 3 4 4 3 2 1], and used the de-bugging step, to view it step by step, and it skips past the if statement on line 18 " if ((find(M(i,:)==val(i)))==1) " whereas this should return a match with the value of 4 at index 4 to the value of 4 at indedx 5. I can not work out why it is skipping back this - i.e. returning a negative for the find value. Many thanks in advance :) (for more background the function is trying to find a saddle point, I'm aware it's probbaly not optimal etc but I think it's best if I learn that myself, and for now if someone could just address my question above. Many thanks ! )
function[indices]=checkingrow(M)
[ b1 b2] = size (M);
%for each row get vector of values
%and vector of indexes seperately
indices=[0,0];
for i=1:b1;
[val(i)]=max(M(i,:));
[~, c]=max(M(i,:));
[k,l]=min(M(:,c));
if l==i
indices=[i,c]
if ((find(M(i,:)==val(i)))==1)
[ind(i)] = find(M(i,:) == val(i))
[z,w]=min(M(:,ind(i)));
if ind(i)==w
indices2=[i,w]
end
end
else indices=indices;
end
end
if indices==[0,0]
indices=zeros(b1,b2)
end
end
  1 个评论
Jan
Jan 2020-11-24
编辑：Jan 2020-11-24
You forgot to mention, what the code should do. The readers cannot guess this detail.
Omit the useless code indices=indices;
Combine the code:
[val(i)]=max(M(i,:));
[~, c]=max(M(i,:));
to
[val(i), c] = max(M(i,:));

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回答（1 个）

Jon
Jon 2020-11-24
编辑：Jon 2020-11-24
I'm not sure exactly what you are trying to do, but I will try to explain what your statement is doing and why it might not be what you intended, here is your statement
((find(M(i,:)==val(i)))==1)
just to be concrete, suppose for example M(i,:) = [1 8 4 2 7 4] and val(i) = 4 then
M(i,:)==val(i)
will give a logical vector [false false true false false true]
performing a find on this will return the indices where the logical vector is true, so
find(M(i,:)==val(i))
will return the vector [3,6]
finally
find(M(i,:)==val(i)))==1
will return a logical vector whose elements are true where the vector [3,6] is equal to 1, so
[false false], since neither 3 or 6 equals 1
Your statement will only evaluate to true if the first element of M(i,:) equals val(i)
By the way, if you select all of your code and then right click and select smart indent your code will be much more readable.

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