Calculating Error Estimates

[davidf(at)dfanning.com (David Fanning)]

Hi Folks,

It is so hot in Colorado today that I think my brain has
vapor locked. In any case, I can use some help. :-)

Here is my problem. I have some experimental data. I
have used CURVEFIT and my roll-your-own function to
fit a curve through the data. What I want to do is
display the experimental data on the plot, along with
the curve. But I want to place error bars through
the experimental data points. My question is this:
how do I calculate the errors for the individual
points so that I can place them on the plot with
ERRPLOT?

CURVEFIT returns to me a parameter called SIGMA,
which contains the standard deviations of the returned
values of the four coefficients in my fitting
function. What I cannot seem to work out is how
to use these standard deviations to obtain an
error estimate for each individual experimental
point.

I realize this is basic error analysis, but even
an hour spent refreshing myself with Bevington
has not successfully stimulated this reptilian brain. :-(

Let's just say I had too much fun on vacation...

Thanks,

David
-- 
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438
Coyote's Guide to IDL Programming: http://www.dfanning.com/