Hi,

I have correlated residuals that are well described by an exponential
function.  However, they exhibit negative spatial autocorrelation at short
lags that decreases to little spatial autocorrelation at longer lags.  I
have fit exponential functions to the residual variograms that fit well,
but the range must be negative to achieve the fit.  I have been searching
the nlme source code for an hour, and have found corExp (and corStruct and
similar things) mentioned multiple time, but have not found how to
eliminate the condition that the range be > 0.  Can anyone point me
generally in the correct direction?  I will likely cause a cascade of
errors if I even get that first part to work.  But just trying to move in
some direction for now.  Thanks. -Seth Myers

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