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Topic: second largest element in a matrix
Replies: 32   Last Post: May 5, 2013 10:31 AM

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Walter Roberson

Posts: 7,673
Registered: 1/20/06
Re: second largest element in a matrix
Posted: Apr 3, 2009 11:09 PM
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Matt Fig wrote:
> This may work though. The speed gain over the sorting is not tremendous because max is called twice.
>
> R = temp; % Preserve R.
> R(~(R~=max(R))) = NaN;
> [c,i] = max(R);


Depends on the matrix sizes. max() is an order(N) operation. sort is something like
order (N*log(N)). With large matrices, two linear passes through the matrix would be
considerably faster than a sort().

Note: in previous postings, someone posted a reference to a linear-time routine
to find the "Q largest" values in a vector; that code would only pass through the
matrix once (but might make up to Q comparisons at each point in order to establish
the proper ordering.)


Date Subject Author
9/18/08
Read second largest element in a matrix
Oluwa KuIse
9/19/08
Read Re: second largest element in a matrix
stephanie
9/19/08
Read Re: second largest element in a matrix
Steven Lord
9/19/08
Read Re: second largest element in a matrix
Oluwa KuIse
9/19/08
Read Re: second largest element in a matrix
Pekka
9/19/08
Read Re: second largest element in a matrix
Oluwa KuIse
9/21/08
Read Re: second largest element in a matrix
Greg Heath
9/24/08
Read Re: second largest element in a matrix
Walter Roberson
3/4/09
Read Re: second largest element in a matrix
Justin
4/6/09
Read Re: second largest element in a matrix
Bruno Luong
4/6/09
Read Re: second largest element in a matrix
Jos
4/6/09
Read Re: second largest element in a matrix
Bruno Luong
4/6/09
Read Re: second largest element in a matrix
Bruno Luong
4/6/09
Read Re: second largest element in a matrix
mike zander
4/7/09
Read Re: second largest element in a matrix
Bruno Luong
4/7/09
Read Re: second largest element in a matrix
Bruno Luong
4/3/09
Read Re: second largest element in a matrix
Paul
11/7/12
Read Re: second largest element in a matrix
sssbi2009@gmail.com
11/19/12
Read Re: second largest element in a matrix
dpb
4/3/09
Read Re: second largest element in a matrix
Paul
4/3/09
Read Re: second largest element in a matrix
mike zander
4/3/09
Read Re: second largest element in a matrix
mike zander
4/3/09
Read Re: second largest element in a matrix
mike zander
4/3/09
Read Re: second largest element in a matrix
Walter Roberson
4/3/09
Read Re: second largest element in a matrix
mike zander
5/4/13
Read Re: second largest element in a matrix
tilindg1@gmail.com
5/4/13
Read Re: second largest element in a matrix
Nasser Abbasi
5/4/13
Read Re: second largest element in a matrix
dpb
5/5/13
Read Re: second largest element in a matrix
Nasser Abbasi
5/5/13
Read Re: second largest element in a matrix
dpb
5/5/13
Read Re: second largest element in a matrix
Bruno Luong
5/5/13
Read Re: second largest element in a matrix
Nasser Abbasi
5/5/13
Read Re: second largest element in a matrix
Bruno Luong

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