Multiple Curve Fitting Program HP-41

[Dieter]

(01-13-2018 09:42 AM)Graan Wrote:  Yes thats more what Im looking for.
...
What I thought however when looking at Kolb's program was that I could feed in X and Y values and the program would select the function with best fit automatically. Is this the case?

Of course I can't say anything about the program in the Kolb book, but if you only want to fit an XY-curve with two parameters and choose between a linear, logarithmic, exponential and power fit, and you already have a DM42, why do you think you need a special program? The HP42s (and I suppose DM42 as well) can do this on their own, including the selection of the best fitting model:

Clear the summation registers with CLΣ
For all data pairs: enter Yi ENTER Xi and press Σ+
Press STAT > CFIT > MODL > BEST and see the best-fitting model marked with a "▪"
Of course you can also select a different model if you prefer
Return to the previous menu with EXIT
SLOPE and YINT show the two regression coefficients
CORR shows the correlation coefficient (indicates how well the model fits the data)
FCSTY calculates the y-estimate for a given x
FCSTX calculates the x-estimate for a given y

Example:

Code:

X:  1   3   5   8
Y:  1   5   10  20

CLEAR > CLΣ
 1 ENTER 1  Σ+
 5 ENTER 3  Σ+
10 ENTER 5  Σ+
20 ENTER 8  Σ+

STAT > CFIT > MODL > BEST 
=>  LINF  LOGF  EXPF  PWR▪

So the best fit is a power function.

Code:

EXIT

SLOPE => 1,4367...
YINT  => 1,0073...

CORR  => 0,9999...

So the regression function is  y = 1,007 · x^1,437.
And the correlation coefficient shows that this is a very good fit.

Now check how well this model fits the given data:

Code:

1 FCSTY =>  1,007...
3 FCSTY =>  4,883...
5 FCSTY => 10,172...
8 FCSTY => 19,985...

Is this what you are looking for?

Dieter