[Numpy-discussion] Upper and lower envelopes

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.