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-   -   warning: zero character (https://www.mersenneforum.org/showthread.php?t=11630)

fivemack 2009-03-21 10:46

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
[/code]

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.


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