Re: grid3 and ill-conditioned matrix stuff

["Richard G. French" <rfrench(at)wellesley.edu>]

tbowers wrote:
> An example of my data. xData, yData, zData, vData in 1st, 2nd,
> 3rd, 4th columns respectively. xData, yData, zData are in
> same units (meters).
> 
> xData         yData            zData      vData
> 
> 573777.43   4344653.40   00.8   2.82174045
> 573777.43   4344653.40   00.9   2.82353044
> 573777.43   4344653.40   01.0   2.81546044
> 573777.43   4344653.40   01.1   2.81331551
> 573777.43   4344653.40   01.3   2.80542541
> 573777.43   4344653.40   01.4   2.80256045
>

If all of your x values are so close to 573777.
and y values are close to 4344653., try as a start
just subtracting the mean values of each of these
arrays from the array itself. I think you may be
running into roundoff problems. You could also try
to cast these arrays as double precision and see
if that helps, but it may be that the internal
workings of trigrid aren't all in double precision.

Dick French