warning: zero character

fivemack · 2009-03-21, 10:46

I've never seen this message before, but when building the matrix for a relatively large factorisation (32-bit large primes on both sides) I got

Code:

using 20 quadratic characters above 1624473360
warning: zero character
warning: zero character

I don't know if the matrix is any good - the job was using 9.5G on an 8G machine and running incredibly slowly, and my 12G machine has jobs on it meaning it doesn't have 9.5G free - but I'm a bit surprised by the message.

jasonp · 2009-03-21, 14:26

I figured this was inevitable when jobs started using 32-bit large primes. The code choses quadratic characters from the primes larger than the largest factor of the algebraic sieve values. When you allow 32-bit large primes, there is a danger that some of the quadratic characters will overflow the 32-bit size and wrap around to the smallest primes.

This isn't a fatal error, it just means that any quadratic characters that wrap around will be useless during the linear algebra. As long as you get 5-7 characters that don't do that, it should be enough for the square root phase to work correctly. If you see that warning a large number of times, you may have to modify the code and rerun the matrix building step.

2009-03-21, 10:46	#1
fivemack (loop (#_fork)) Feb 2006 Cambridge, England 1913₁₆ Posts	warning: zero character I've never seen this message before, but when building the matrix for a relatively large factorisation (32-bit large primes on both sides) I got Code: using 20 quadratic characters above 1624473360 warning: zero character warning: zero character I don't know if the matrix is any good - the job was using 9.5G on an 8G machine and running incredibly slowly, and my 12G machine has jobs on it meaning it doesn't have 9.5G free - but I'm a bit surprised by the message.

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2009-03-21, 14:26	#2
jasonp Tribal Bullet Oct 2004 DD5₁₆ Posts	I figured this was inevitable when jobs started using 32-bit large primes. The code choses quadratic characters from the primes larger than the largest factor of the algebraic sieve values. When you allow 32-bit large primes, there is a danger that some of the quadratic characters will overflow the 32-bit size and wrap around to the smallest primes. This isn't a fatal error, it just means that any quadratic characters that wrap around will be useless during the linear algebra. As long as you get 5-7 characters that don't do that, it should be enough for the square root phase to work correctly. If you see that warning a large number of times, you may have to modify the code and rerun the matrix building step.