135
Choosing from available fit models
On the hp 39g+ the Statistics aplet is the only
one which has a SYMB SETUP view, and even then
only in mode. This view is supplied to allow
you to specify what type of fit equation is to be used.
The choices are:
Linear - m*X+b (YmXb
+ )
Logarithmic - m*LN(X)+b (
)
lnYm X b
+
)
Exponential - b*EXP(m*X) (
mX
Ybe= )
Power - b*X^m (
m
YbX= )
Quadratic - a*X^2+b*X+c (
2
YaX bXc
++
)
Cubic - a*X^3+b*X^2+cX+d (
32
YaX bX cXd
+++)
Logistic - L/(1+a*exp(-b*X)) this fits the data to a logistic
curve (
1
bX
L
Y
ae
−
=
+
) where L is the saturation value.
(see tip below)
and - User Defined - discussed below.
Calculator Tip
1. If you want L calculated automatically, pre-store a value
of zero into it. If the value is known, you can store a
positive real value into memory L prior to the curve fit.
2. If you calculate a line of best fit and want to remove the
resulting equation from the SYMB display and return to
the ‘m*X+b’ display then just position the highlight on
the relevant ‘Fit:’ line and press the DEL key. When
you do this, the will be removed and will have to
be reset.
The User Defined model
When you set the model to user defined it
means that you are expected to supply the
complete equation, including the values of any
coefficients. The calculator will not calculate the values of any variables you
include. For example, if you were to supply an equation of /( )
XB
as your
model then the calculator would use the values of A and B currently in
memory.
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