Advantage Pac Curve Fitting


After the regression coefficients have been calculated, projections may be made based on the curve fit. I'm disappointed that you may only key in an x value to see an estimated y value. How about keying in a known y value? I thought about adding this feature to the CFIT program, similar to the Curve Fitting program originally published in the HP-67 Standard Pac. Are there any issues with running a tweaked program from main memory, with the advantage pac still installed?


Projecting Y onto X may seem harmless from a mathematical point of view. However, some statistician may frown upon that, because (the way I understand it) the measurement in variable X have no error in its measurement while those of variable Y has normally distributed errors. For some reason statisticians frown on calculating X^ ... and the really get into a hissy fit (pun intended) if you calculate the confidence interval of X^.


Edited: 21 June 2011, 8:17 p.m.


Well, suppose you measure the gross weight of a UPS truck (y) with various numbers of packages (x) in it, and you get the regression equation ˆy = 2.17x+2463. The slope, 2.17, is the average weight per package, and the y intercept, 2463, is the weight of the empty truck. The value of ˆy when x is 0 isn't always meaningful, but in this case, it has physical meaning!

Edited: 21 June 2011, 10:36 p.m.


From what I've read it's not the same if you just invert the resulting regression equation as opposed to swapping x and y in the data set and do a new regression to predict x from y. So in order to do it correctly, you need to accumulate the reverse statistic in parallel for this kind of calculation.


You were asking about supplying a value for Y and calculating X. Some statisticians will cry foul because the relation of the regression line is to correlated Y with X and not X with Y.


The point I was trying to make is that a least squares fit has applications other than statistics. For instance, I use it to iterate between finite element analyses results, when determining the starting point for the next iteration. The relation between X and Y is not statistical, but is based on geometry and material properties used in the model. If the material(s) have a linear stress-strain relationship, then the straight line fit would represent the combined spring rate (for complex models this would be difficult to calculate directly). And geometry can introduce non-linear behavior (e.g. belleville spring). For such uses, it would be nice to have the option to calculate estimates in either direction, where Y=load and X=deflection.

Edited: 22 June 2011, 8:48 a.m.


Makes sense to me.


The HP 20s has (IMHO) both!

Just to bad it hasn't RPN.


The HP-33s and HP-35s provide the capability you want and have rpn.


I modified the CFIT program over the weekend to include Y predictions. One thing I noticed is that if you call the subroutines (e.g. "A~", BFIT, etc.) from the module and get an error, a R/S will continue execution from within the unmodified CFIT program.

Possibly Related Threads...
Thread Author Replies Views Last Post
  HP67/97 M.E. Pac cover Ignacio Sánchez 2 767 11-22-2013, 04:04 AM
Last Post: Ignacio Sánchez Reig
  request M.E. pac for HP-67/97 wallet cover scan Ignacio Sánchez 0 548 11-06-2013, 09:36 AM
Last Post: Ignacio Sánchez Reig
  HP-67/97 Mechanical engineering PAC cover Ignacio Sánchez 0 512 10-30-2013, 04:35 AM
Last Post: Ignacio Sánchez Reig
  Entering,Saving,and Analysis /Fitting X Y Data on the Prime Harold A Climer 6 1,262 10-26-2013, 01:54 PM
Last Post: Tim Wessman
  Challenge(?): Intersection curve between two cylinders in a specific position Pier Aiello 15 2,019 09-17-2013, 05:58 PM
Last Post: Pier Aiello
  HP Prime : geometry & curve Mic 0 484 09-15-2013, 02:31 PM
Last Post: Mic
  HP41 Navigation Pac Perpetual Alminac Dan Pfeiffer 2 731 09-03-2013, 07:39 PM
Last Post: Dan Pfeiffer
  Advantage/CCD Matrix Challenge Ángel Martin 1 622 08-09-2013, 06:22 PM
Last Post: Thomas Klemm
  HP 32S-II Vertical Curve Program Ron Cardwell 2 732 05-20-2013, 07:54 AM
Last Post: Thomas Klemm
  HP 41CX Survey Pac Keith Burr 7 1,277 03-29-2013, 10:09 AM
Last Post: Keith Burr

Forum Jump: