Using .' instead of ' for transpose

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Andrew
Andrew 2014-7-14
评论： Andrew 2014-7-14
Hello, this is somewhat of a theory question.
I am wondering why I frequently see .' instead of just ' when computing the transpose of a matrix. I performed some tests myself and saw that this is generally a little faster but why is it faster? what is the difference in the internal implementation of .' as opposed to just '?
I've just been wondering about this and wanted to see what other people's thoughts are.

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Azzi Abdelmalek
Azzi Abdelmalek 2014-7-14
编辑：Azzi Abdelmalek 2014-7-14
.' is used to transpose complex numbers, because if for example a is a complex array
a=[4+5i 2-i]
a' % is the conjugate and transpose
a.' % is the transpose
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Andrew
Andrew 2014-7-14
Ah, I see, that makes sense but why then is .' faster? Is it because it doesn't check for complex numbers?

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James Tursa
James Tursa 2014-7-14
For complex matrices, see Azzi's answer. You are doing a little extra work for the conjugate part.
For real matrices, I don't know that there is any difference in implementation. In fact, I would expect both to call exactly the same underlying routine to do the work. I would suspect that any difference in run times you are seeing is quite small and if you make several tests you will see a variation in both methods but not much difference between the methods.
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Andrew
Andrew 2014-7-14
Thanks James,
I tried running some more tests and the times eventually did converge to almost exactly the same for a 1000 by 1000 matrix.

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