Permute N-D array : why is it faster with real than complex ?

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Richard
Richard 2014-6-20
回答： Richard 2014-6-23
Hi!
I'm encoding a matlab function which calculate the contraction of two tensor. It's quite good but I have a problem with permute : it's faster with real than complex. For example :
>> A=rand(250,10,500,120);
>> B=complex(rand(250,10,500,120),rand(250,10,500,120));
>> sigma=[3 4 1 2];
>> tic; A=permute(A,sigma); toc
Elapsed time is 0.945218 seconds.
>> tic; B=permute(B,sigma); toc
Elapsed time is 3.444950 seconds.
Do you know why is there such a gap ? Can you help me reduce it ?
Thanks!
PS : I'm sorry, my English is not good....

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采纳的回答

Matt J
Matt J 2014-6-20
编辑：Matt J 2014-6-20
Do you know why is there such a gap ?
Because there is twice as much data to shuffle around when you have both real and imaginary parts.
Can you help me reduce it ?
Assuming you can tolerate lower precision, you could use type single instead of type double. On my machine,
>> tic; permute(B,sigma); toc
Elapsed time is 0.872804 seconds.
>> B=single(B);
>> tic; permute(B,sigma); toc
Elapsed time is 0.582679 seconds.

更多回答（1 个）

Richard
Richard 2014-6-23
Thanks for your answer. It's better but not enough for my problem. I've to try another way, without permutation.

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