John, I reckon I misquoted my dodgy formula which gave me the large numbers.
I'm sure I had the ^{...} on the x's. In any case. I've got it to work on my
full data set now, so that's my original question well answered.For your curiosity, the x's were wind speed and the y's were noise level. (LA90,10 mins) The guidance, dating back some years, talked of a using polynomials of no more than 5th order to fit the data, but a recent article (written by proper statisticians and not mere acousticians!) warned of the dangers of overfitting the data - maybe 500 points with lots of scatter) Using even a cubic means that at low wind speeds you are predicting the the noise level flies up again and that high wind speeds the noise level could drop off again, so they used to say, just do a piecewise solution and limit the curve flat at the max and min. The latest advice is to ensuring that your curve reaches a sensible level (15? 17? 20?) at zero windspeed by using a even-number-powered polynomial and constrain the slope at/near x=0. Thanks for your help. -- View this message in context: http://gnome-apps.13852.n7.nabble.com/Constrain-a-polynomial-trend-line-to-intercept-y-axis-horizontally-tp63654p63665.html Sent from the GnuMeric mailing list archive at Nabble.com. _______________________________________________ gnumeric-list mailing list gnumeric-list@gnome.org https://mail.gnome.org/mailman/listinfo/gnumeric-list
