20200213, 04:47  #1 
Aug 2006
3×1,993 Posts 
Parity barrier
Silverman suggested talking about some real mathematics, maybe the parity problem. I don't know if we have enough expertise here for a good discussion, but I thought I'd give it a go.
Tao has some great expository articles: https://terrytao.wordpress.com/2007/...sievetheory/ https://terrytao.wordpress.com/2014/...mobstruction/ https://terrytao.wordpress.com/2015/...sievetheory/ https://terrytao.wordpress.com/2014/...boundederror/ https://terrytao.wordpress.com/2016/...mptoticsieve/ Here are some papers showing real results breaking the parity barrier: Friedlander & Iwaniec, HeathBrown, Helfgott, HeathBrown & Moroz, RamarĂ© & Walker, Tao, and Zhang. It's hard,and there are still no general techniques, but it's doable. Bilinear forms seem to be a recurring theme. 
20200213, 05:09  #2  
Nov 2003
7460_{10} Posts 
Quote:
element to the sieve a tiny bit of error creeps in. With enough elements the error term overtakes the main term. Typically, when sieving integers up to B is that one can use up to [log(B)]^m for some m elements in the sieve or under some conditions B^epsilon for small epsilon before the errors become too large. This is known sometimes as the "fundamental lemma of the sieve". Example: How many integers in [1,101] are divisible by 3. Answer is trivially 33. But it is also 33 for [1,99], and [1,100]. We estimate the number in [1,N] as N/3 but this is seen to be a "little bit wrong". If we want to sieve all the primes up to K without error we need to take B >> 2*3*5*...K ~ exp(K). Thus we only are allowed to have log(B) primes in the sieve if we want to avoid accumulating errors. When we bound the error (depending on the weighting scheme) we can take up to log^m (B) sieve elements. 

20200213, 05:49  #3  
Nov 2003
2^{2}·5·373 Posts 
Quote:
for these forms have "sufficient density". When one considers (say) X^2 + 1, there are ~sqrt(B). such integers up to B. But if we take a bilinear form such as x^2 + y^4 there are ~B^(3/4) such integers less than B. This is "just enough more" so that sieve methods can succeed; the range sets are just a little bit denser. BTW, I have read Halberstam & Richert's "Sieve Methods" a couple of times. I have it on good authority from an expert (my ex) that it is a great reference, but not a great textbook to learn from. I found it frustrating to read and understand. I still can't claim to understand it, but it is a good starting point. 

20200213, 05:52  #4  
Nov 2003
1110100100100_{2} Posts 
Quote:


20200215, 03:07  #5 
Aug 2006
3·1,993 Posts 

20200217, 03:38  #6 
Nov 2003
2^{2}×5×373 Posts 

20200222, 00:43  #7 
"Phil"
Sep 2002
Tracktown, U.S.A.
3·373 Posts 

20200225, 16:20  #8 
Nov 2003
7460_{10} Posts 

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