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[WP34s] Linear and non-linear regression with L.R.
05-22-2014, 07:39 PM (This post was last modified: 05-22-2014 07:43 PM by Dieter.)
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[WP34s] Linear and non-linear 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 a0 and a1. But it does not say where which coefficient is returned. #-) After some tests it seems that a0 is returned in X and a1 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 a0, it is ln a0. 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 = ex this should yield 1 for a0 as well as a1. But instead a zero is returned in X.

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[WP34s] Linear and non-linear regression with L.R. - Dieter - 05-22-2014 07:39 PM

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