Asked by Diego Yanez
on 16 Jan 2013

I have a fairly large vector named blender (45,000+). I have extracted n elements for which blender is greater than b (irrelevant). Now my difficulty is the following:

I am trying to create a 21 x n matrix with each extracted element of blender plus 10 things before, and the 10 things after, hence the reason why each column is 21.

I have been trying variations of the following:

element=find(blender >= 120);

NewMatrix = zeros(21, length(element)); for i = 1:length(element) k = element(i); NewMatrix(:,i)= Matrix(blender(k-10:k+10)); end

then I want to plot one column of the matrix at the time when I hit Enter. This second part I can figure out later, but I would appreciate some help making the Matrix

Thanks

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Answer by Cedric Wannaz
on 16 Jan 2013

Edited by Cedric Wannaz
on 16 Jan 2013

Accepted answer

If I understand well and if you want to keep it simple with an explicit for loop, what you want to do is something like that I guess:

element=find(blender >= 120);

NewMatrix = zeros(21, length(element)); for ii = 1:length(element) k = element(ii); r = max(1, k-10) : min(length(blender), k+10) ; % Range of indices +/- 10 % limited to valid ids. NewMatrix(1:length(r),ii) = blender(r); % Store blender on the % valid range; next % elements left to 0. end

Cheers,

Cedric

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Cedric Wannaz
on 16 Jan 2013

You're welcome! About how it works, I just followed your initial idea indeed. The logic is as follows:

- You want to extract blocks from
`blender`at each`k`+/-10,`k`going iteratively through all indices returned by find(). - During iteration
`ii`, you want a priori to perform something like:`NewMatrix(:,ii) = blender(r)`,`r`being the set/range of indices that cover the block`k`+/-10. This is almost what you implemented. - Now there is a small additional difficulty; if
`k<=10`,`k-10`is not a valid index (below 1). In other words, when k is too close to element 1 of`blender`, this "window" that you want to extract must be truncated. The same applies when k is close to the end of`blender`. - For this reason, we define
`r`that is this window, truncated when it has to. - Now when there is truncation,
`blender(r)`is not 21 elements long, so you cannot store it in`NewMatrix(:,ii)`as the`:`addresses the full length of`NewMatrix`along the first dimension, which is 21. So we have to replace`:`with a vector of indices whose length equals the length of`r`.

Diego Yanez
on 17 Jan 2013

Any chance you can help with the second part of my question. I want to plot one column of NewMatrix at the time, cycling through the next column when I hit Enter. This is as far as I got:

for j=1:length(element) figure(1) plot(NewMatrix(:,j),'bo--') grid on keyboard end

This stops at the first column, but does not keep cycling

Opportunities for recent engineering grads.

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