[SI-LIST] Re: non-negative off diagonal capacitive matrix elements ??

Ray,

I have seen such issues with other simulators ... but at the time those
numbers were very weekly positive. I was looking at  self caps worth a
pF and some non-diagonal elements that were in the range of 1e-6 pF or
so. Observing that the positive number you got is between the farthest
two elements, is there a chance it could be just a "rounding of error"
type thing, where it really should be zero, but it comes out slightly
positive.

Looking at your data, the bulk (self?) cap is 3.16 fF, the positive
mutual you see is 0.00003 fF (100,000 times smaller)... seems to me it
is really zero, but the small numerical error in the simulator put it
weakly positive.

Regards,

- Neeraj.

National Semiconductor Corporation
2900 Semiconductor Drive, Mail Stop 19-100
Santa Clara, California 95051

Ray Anderson wrote:

> I've just extracted the RLGC matrices for 5 coupled
> striplines using Apsimtech RLGC.
>
> As expected, the diagonal elements of the capacitive matrix are
> positive capacitance values. All the off-diagonal elements are
> negative EXCEPT one. Is this correct. It has been a while since I've
> thought about this, but I was under the impression the capacitive
> off diag element were all negative. Anyone know for sure ??
>
> The element in column 1 row 5 is the one I question:
>
>    3.1600e-15
>   -4.9360e-16   3.2540e-15
>   -2.0080e-17  -4.8990e-16   3.2540e-15
>   -1.3380e-18  -1.9820e-17  -4.8990e-16   3.2540e-15
>    3.1280e-20  -1.3380e-18  -2.0080e-17  -4.9360e-16   3.1600e-15
>
> -Ray
>
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