Texas Instruments TI-83 PLUS - Manual (Page 365)

TI-83 Plus Statistics 362
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.
Note: The output of SinReg is always in radians, regardless of the Radian/Degree
mode setting.