Logical XOR (Migrated from community.research.microsoft.com)

# Logical XOR (Migrated from community.research.microsoft.com)

• venerdì 3 giugno 2011 18:43
Proprietario

vtan posted on 03-31-2011 8:28 PM

Hi John,

I'm using Infer.NET to solve a decoding problem in GF(2). I am trying to do a logical XOR of  Variable<bool>[ ] m, since there's no inbuilt logical XOR. I've attached the code to the end of this message. It compiles fine but the inference results are not symmetric in the arguments of the array m, when I think it should be since GF(2) + (or logical XOR) is commutative. Any help would be appreciated.

Thanks,

Vincent Tan

s1 = gf2sum4vectors(m1);

private Variable<bool> gf2sum4vectors(Variable<bool>[] m)
{
Variable<bool>[] partialSums = new Variable<bool>[m.Length];
for (int i = 0; i < m.Length; i++)
{
if (i == 0)
partialSums[i] = m[0];
else
partialSums[i] = gf2sum(partialSums[i - 1], m[i]);
}

return partialSums[m.Length - 1];
}

private Variable<bool> gf2sum(Variable<bool> a, Variable<bool> b)
{
return ((a & (!b)) | (b & (!a)));
}

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• venerdì 3 giugno 2011 18:43
Proprietario

John Guiver replied on 04-01-2011 10:18 AM

Hi Vincent

Have you seen the following post: http://community.research.microsoft.com/forums/t/4202.aspx? This discusses how to do XOR for single variables - i.e. your gf2sum method. Try that, and if there are still problems, please repost.

John

• venerdì 3 giugno 2011 18:43
Proprietario

vtan replied on 04-01-2011 10:46 AM

Hi John,

(a!=b) is a nice way of implementing XOR. Strangely though, in my application, doing (a & !b) | (b & !a) yields results that are more correct. I can't explain why.

Vincent