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Old 2017-03-18, 10:51   #1
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"Matthew Anderson"
Dec 2010
Oregon, USA

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Default Goldbach's weak conjecture

Hi Mersenneforum,

The 3 primes problem, or weak Goldbach conjecture has been proved true by
Helfgott in 2013.

It simply states that all odd numbers < 7 are the sum of 3 odd prime numbers.


In My Humble Opinion (IMHO) this was quite a proof.

wanted you to know.

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Old 2017-03-18, 23:32   #2
CRGreathouse's Avatar
Aug 2006

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Greater than 7, that is.

Yes, it was a big deal! The proof had three parts: major arcs, minor arcs, and verifying weak Goldbach on small values. The third part was joint work with Platt and was verified considerably further than necessary: to 8.875e30 when Helfgott needed only 10^27.

Here's my understanding of the major+minor arc decomposition. Instead of looking at the sum
of the number of ways a given odd number N can be written as a sum of three primes, Helfgott looks at the related sum
\sum_{p+q+r=N}\log p\log q\log r
which is a weighted version of the first which is easier to work with analytically.

Next the sum is transformed into an integral
\int_0^1 S(\alpha,x)^3 - \exp(-2\pi iN\alpha)d\alpha
which is then split into two pieces: the major arcs, which are small intervals around rationals with small denominators, and the minor arcs which are everything else.

Actually, the integral Helfgott actually uses is a somewhat more complicated 'smoothed' version of this integral, but the basic idea is the same: it can be broken into major and minor arcs, and proving that it takes on positive values for a given N shows that weak Goldbach holds for that N.

Helfgott spends a paper describing how to bound the minor arcs very precisely, then has a somewhat easier task (because of the groundwork he laid) on the major arcs. Combining the two Helfgott proves that the smoothed integral is at least 0.000422 * N^2 when N is an odd number greater than 10^27, which together with the numerical verification with Platt proves the weak Goldbach conjecture.

Helfgott cites a lot of software used in the proof including PARI, Maxima, Gnuplot, VNODE-LP, PROFIL / BIAS, SAGE, and Platt’s interval-arithmetic package (based in part on Crlibm).
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