dec2bin

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Talaria
Talaria 2011-8-5
how do i overcome the limitation of dec2bin of 2^52??
saying i would need to convert numbers greater than 2^52. or is there another possible way to generate all possible binary values of one length. for example: length =3 000, 001, 010, 011, 100, 101, 110, 111.

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回答（4 个）

Arnaud Miege
Arnaud Miege 2011-8-5
It seems to work for me:
>> dec2bin(2^52)
ans =
10000000000000000000000000000000000000000000000000000
>> dec2bin(2^52+1)
ans =
10000000000000000000000000000000000000000000000000001
Arnaud
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Talaria
Talaria 2011-8-5
thanks alot, but how to overcome this problem??
Jan
Jan 2011-8-5
@Talaria: Which problem do you want to solve exactly? The limitation of DOUBLEs to 53 bit precision can be solved by using UINT64 variables, which allows numbers until 2^64-1. But there will still be the problem, that the number of permutations exceeds the power of current computers dramatically. In other words: There is no way to solve your problem by brute force. To suggest a smarter solution, it is necessary, that you explain the actual problem with any details at first.

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Jan
Jan 2011-8-5
A fast method to create permutations with order and repetition is FEX: VChooseKRO-mex:
M = VChooseKRO(uint8([0, 1]), 3)
The UINT8 values need 1/8 of the memory occupied by DOUBLEs.
But if you need all permutations with 52 elements, you need some free RAM: 2^52*52 Bytes = 2.34 TB...
Walter Roberson
Walter Roberson 2011-8-5
With regards to a list of all possible binary values of a given length:
If the length desired is N, there are 2^N such values. You want the dec2bin representation of each, which requires one char per original bit. In MATLAB each char requires 2 bytes, so the required storage would be 2^N * 2 = 2^(N+1) bytes.
According to Wikipedia, the current x86_64 architectures implement only 48 bits of addressing space. If you could find a system that implemented and populated all 48 bits of memory, and there was no overhead associated with the storage of the values, then your limit would be N+1 = 48, which would be N=47 -- the best you could hope to do would be to dec2bin() all of the 47 bit numbers, and that would take you 2^48 bytes which would be 256 TB.
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Jan
Jan 2011-8-5
@Talaria: In addition the calculations will need some years.

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Fangjun Jiang
Fangjun Jiang 2011-8-5
I'd like to put the question this way. See the example first.
>> dec2bin(2^55+[0 1 2 3 4 5 6 7 8 9 10 100 1000])
ans =
10000000000000000000000000000000000000000000000000000000
10000000000000000000000000000000000000000000000000000000
10000000000000000000000000000000000000000000000000000000
10000000000000000000000000000000000000000000000000000000
10000000000000000000000000000000000000000000000000000000
10000000000000000000000000000000000000000000000000001000
10000000000000000000000000000000000000000000000000001000
10000000000000000000000000000000000000000000000000001000
10000000000000000000000000000000000000000000000000001000
10000000000000000000000000000000000000000000000000001000
10000000000000000000000000000000000000000000000000001000
10000000000000000000000000000000000000000000000001100000
10000000000000000000000000000000000000000000001111101000
From the help of uint64:
The values of a UINT64 range from 0 to 18,446,744,073,709,551,615,
(that is, from INTMIN('uint64') to INTMAX('uint64')). Values outside
this range are mapped to INTMIN('uint64') or INTMAX('uint64').
NOTE: The range of values that can be passed to UINT64 from the command
prompt or from an M-file function without loss of precision is 0 to
2^53, inclusive. When reading values from a MAT-file, UINT64 correctly
represents the full range 0 to (2^64)-1.
So, not to ask to generate all the possible binary values of a 55-bits binary number, but, is there a way in MATLAB to generate the binary string of two numbers, say (123+2^55) and (456+2^55) and see the exact difference?
The values are still within 2^64-1 so it should be possible. But how to do it? It sounds like need to write the binary number to a .mat file and then load it back?
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Walter Roberson
Walter Roberson 2011-8-5
You need R2011a or later in order to do arithmetic on 64 bit numbers. R2010b extends uint64() to be able to handle hard-coded constants of more than 53 bits, but R2010b does not handle arithmetic on these numbers.
There are ways to handle the computation as uint32 values, but that's usually a nuisance to code directly.
If John d'Errico's "vpi" is still in the file exchange, that could be used.

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