Re: hp41 howto do simple linear regression? Message #2 Posted by Dave Shaffer on 17 Dec 2002, 8:02 p.m., in response to message #1 by David E
Well, David, you can always do it the semihard way  with just the '41 itself.
If you use the sigma+ button (top left on the keypad)(after clearing the summation registers using the CLSigma button  shift x<>y key, just below the sigma+ key), you can accumulate the sums of x, x^2, y, y^2, and xy in memory registers 11 through 15 respectively, while register 16 will get the value of n (the number of x,y pairs). To put in your numbers, enter y first, then "ENTER", and then enter your x value  then hit the sigma+ key.
After you have entered all you pairs of values, you need to remember (or be told  or, left as an exercise for the student, derive!) the leastsquares fitting expressions for slope, intercept, and correlation coefficient. In case you are rusty:
the slope is (n*SUMxy  SUMx*Sumy)/(n*SUMx^2  (Sumx)^2)
the intercept has the numerator SUMy*SUMx^2  SUMxy*SUMx
(with the same denominator as for the slope)
r is (n*SUMXY  SUMx*SUMy) / ( SQRT(n*SUMx^2  (SUMx)^2) * SQRT(n*SUMy^2  (SUMy)^2) )
I hope my notation is clear. SUMx means the summation of x, and (SUMx)^2 means to square this sum (whereas SUMx^2 means the summation of xsquared).
Have fun.
