Re: What can cause NaN during Conjugate-Gradient iteration (ITL)

Just a guess would be that something is going wrong with the  
preconditioner.  Try the same matrix without a preconditioner and see  
if it still fails.

Cholesky factorization will fail if the matrix is not positive- 
definite -- e.g., you may be trying to take the square root of a  
negative number in the pivot -- or you may have a zero on the  
diagonal.  Check your matrix to make sure it is well-defined for  
(incomplete) Cholesky factorization.


On Apr 8, 2006, at 10:26 PM, Shaun Lademora wrote:

> I am seeing NaN as a result after iteration 0 when doing cg.
>
> I am using the modified_cholesky preconditioner on my input matrix  
> A before calling cg.
> What are potential causes of a NaN result?
>
> Thanks,
> Shaun
>
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