[WP34s] Linear and nonlinear regression with L.R.

05222014, 07:39 PM
(This post was last modified: 05222014 07:43 PM by Dieter.)
Post: #1




[WP34s] Linear and nonlinear regression with L.R.
The 34s offers a L.R. command for various types of regression curves with two parameters. I am not quite happy with a few points:
1. Obviously the function is called "L.R." for historic reasons: earlier HPs like the 34C exclusively offered a Linear Regression, so the command was named accordingly. However, the 34s can do a lot more: It can calculate five different fits, i.e. linear, exponential, logarithmic, a power function, and even "the best of all these". That's why this function should be renamed to something more universal, e.g. REGR. Also the two parameters could simply be called a and b, which would make the whole thing more readable. 2. The PDF manual states that the function returns two regression coefficients a_{0} and a_{1}. But it does not say where which coefficient is returned. #) After some tests it seems that a_{0} is returned in X and a_{1} in Y. This should be added. 3. and most important: the function does not work as described in the manual. For the exponentional and power fit, the result returned in X is not a_{0}, it is ln a_{0}. This should be fixed. Not in the manual, but in the software. Example: try an exponential fit for [0, 1] and [1, e]. Since y = e^{x} this should yield 1 for a_{0} as well as a_{1}. But instead a zero is returned in X. Dieter 

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