Choose function too slow
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Dear All,
i try to run
index=nchoosek(1:200, 10);
it talks a lot of time
is there exist any code that can be more faster.
Thanks in Advance.
回答（4 个）
Image Analyst
2012-9-3
Look at the number of rows it would return:
>> factorial(200)./(factorial(200-10)* factorial(10))
ans =
NaN
>> factorial(200)
ans =
Inf
What do you really want to do. I doubt you need to do it this way. Perhaps rand or randperm might work for you.
1 个评论
Walter Roberson
2012-9-3
The number of possibilities is about 2.2E+16
Walter Roberson
2012-9-3
1 个投票
An array that large cannot be done on any platform supported by MATLAB. It is 22451004309013280 outputs, each 10 entries long. Now, 200 is a number that fits within 8 bits so in theory the individual entries could be a single uint8 (a byte each); that still requires 2^(57.64) bytes of memory. No released x86 CPU has been designed that uses more than 48 bits of memory addressing, so your problem is 2^(ceil(57.64)-48) = 1024 times larger than is possible on any supported platform at this time.
Jan
2012-9-3
0 个投票
FEX: VChooseK is much faster than Matlab's nchoosek. But for your job a really large memory is required. So think twice if you really need such a giantic array.
Hassan
2012-9-3
0 个投票
2 个评论
Walter Roberson
2012-9-3
So see that URL and load in a compiler and SDK.
Jan
2012-9-4
You find several threads about installing a compiler in this forum.
Did you follow my advice to think twice?
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