[WP34s] Linear and non-linear regression with L.R.

[Dieter]

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 = e^x this should yield 1 for a₀ as well as a₁. But instead a zero is returned in X.

Dieter