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improve performance of this code

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Salvatore Mazzarino
Salvatore Mazzarino 2012-11-10
关闭： MATLAB Answer Bot 2021-8-20
suppose to have a matrix called A
3 0 3 3
0 0 4 0
and have this function
while(1)
if all(A(:,i) == 0)
i = i + 1;
else
i = i + 1
break;
end
end
How can I improve the performance of this code?
  2 个评论
Salvatore Mazzarino
Salvatore Mazzarino 2012-11-10
I want to find the index that rappresents the column where there are at least one element

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回答（3 个）

Jan
Jan 2012-11-10
编辑：Jan 2012-11-10
I cannot imagine that you can feel the speedup for such a tiny problem.
k = 1; % Avoid using "i" as variable
while(1)
if any(A(:, k)) % This saves the creation of the temp logical vector
k = k + 1;
break;
else
k = k + 1
end
end
Note that you function will crash, when A contains zeros only. More secure:
index = NaN;
for k = 1:size(A, 2)
if any(A:, k)
index = k;
break;
end
end
Now index is a NaN, if no column matches the condition.
Shorter:
k = find(any(A, 1), 1);
For large A this must be slower, if a matching column appears early.
  1 个评论
Salvatore Mazzarino
Salvatore Mazzarino 2012-11-10
i variable is important in my code. it's incremented during the execution of my code. it cannot be fixed
Matt J
Matt J 2012-11-10
编辑：Matt J 2012-11-10
i = find(any(A,1) ,1)
Azzi Abdelmalek
Azzi Abdelmalek 2012-11-10
编辑：Azzi Abdelmalek 2012-11-10
out= min(find(any(A)))
%or
ii= 1;
while(1)
if any(A(:,ii))
break;
else
ii= ii+1
end
end

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