[Numpy-discussion] Upper and lower envelopes

Anne Archibald peridot.faceted@gmail....
Tue Sep 30 15:37:04 CDT 2008


2008/9/30 bevan <bevan07@gmail.com>:
> Hello,
>
> I have some XY data.  I would like to generate the equations for an upper and
> lower envelope that excludes a percentage of the data points.
>
> I would like to define the slope of the envelope line (say 3) and then have my
> code find the intercept that fits my requirements (say 5% of data below the
> lower envelope).  This would then give me the equation and I could plot the
> upper and lower envelopes.
>
>
> I hope this makes sense.  Thanks for any help.

For this particular problem - where you know the slope - it's not too
hard. If the slope is b, and your points are x and y, compute y-b*x,
then sort that array, and choose the 5th and 95th percentile values.

Anne


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