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improve performance of this code

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Salvatore Mazzarino
Salvatore Mazzarino on 10 Nov 2012
Closed: MATLAB Answer Bot on 20 Aug 2021
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 Comments
Azzi Abdelmalek
Azzi Abdelmalek on 10 Nov 2012
What do you want to find?
Salvatore Mazzarino
Salvatore Mazzarino on 10 Nov 2012
I want to find the index that rappresents the column where there are at least one element

Answers (3)

Jan
Jan on 10 Nov 2012
Edited: Jan on 10 Nov 2012
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 Comment
Salvatore Mazzarino
Salvatore Mazzarino on 10 Nov 2012
i variable is important in my code. it's incremented during the execution of my code. it cannot be fixed

Matt J
Matt J on 10 Nov 2012
Edited: Matt J on 10 Nov 2012
i = find(any(A,1) ,1)

Azzi Abdelmalek
Azzi Abdelmalek on 10 Nov 2012
Edited: Azzi Abdelmalek on 10 Nov 2012
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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