Operation Manual

Chapter 12: Statistics 209
PwrReg—(ax
b
)
PwrReg (power regression) fits the model equation y=ax
b
to the data using a least-squares fit and
transformed values ln(x) and ln(y). It displays values for a and b; when DiagnosticOn is set, it also displays
values for
r
2
and r.
PwrReg [Xlistname,Ylistname,freqlist,regequ]
Logistic—c/(1+a…e
-bx
)
Logistic fits the model equation y=c/(1+a…e
L
bx
) to the data using an iterative least-squares fit. It displays
values for
a, b, and c.
Logistic [Xlistname,Ylistname,freqlist,regequ]
SinReg—a sin(bx+c)+d
SinReg (sinusoidal regression) fits the model equation y=a sin(bx+c)+d to the data using an iterative
least-squares fit. It displays values for
a, b, c, and d. At least four data points are required. At least two
data points per cycle are required in order to avoid aliased frequency estimates.
SinReg [iterations,Xlistname,Ylistname,period,regequ]
iterations is the maximum number of times the algorithm will iterate to find a solution. The value for
iterations can be an integer ‚ 1 and  16; if not specified, the default is 3. The algorithm may find a
solution before
iterations is reached. Typically, larger values for iterations result in longer execution times
and better accuracy for
SinReg, and vice versa.
A
period guess is optional. If you do not specify period, the difference between time values in Xlistname
must be equal and the time values must be ordered in ascending sequential order. If you specify
period,
the algorithm may find a solution more quickly, or it may find a solution when it would not have found
one if you had omitted a value for period. If you specify period, the differences between time values in
Xlistname can be unequal.