Re: [ng-spice-devel] ACS


To ng-spice-devel@ieee.ing.uniroma1.it
From Alan Gillespie <alan.gillespie@analog.com>
Date Wed, 01 Nov 2000 12:06:00 +0000
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Steve Hamm wrote:
> 
> We've seen some real circuits where a 64-bit solution isn't good
> enough. (It isn't too hard to contrive an example where 64 bits isn't
> enough. 64 bits is just 15-ish decimal digits; a circuit where gmin at
> 1e-12 is fighting with milli-ohm resistors is starting to get ugly.)
> Iterative improvement might be helpful for these cases. I've also seen
> a paper from Bell Labs where they used a least-squares solution for
> these nasty situations.

But my understanding is that spice only iterates until
things stop moving within reltol, so surely the final
solution will never be anywhere near accurate enough to
need 64 bits of precision ? So long as the matrix code
produces results accurate to within a few bits at single
precision (is that about 24 bits, i.e. 1 in 16 million)
that'll be way more accurate than the 1 in a thousand
or so that reltol is usually set to.

Am I missing something ?

Cheers,

Alan

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