HP 50g Graphing Calculator - Manual (Page 526)

Page 16-49
The figure below is a box plot of the data produced. To obtain the graph, first
copy the array just created, then transform it into a column vector by using:
OBJ
1 + ARRY (Functions OBJ and ARRY are available in the
command catalog, ‚N). Store the array into variable ΣDAT by using
function STO Σ (also available through ‚N). Select Bar in the TYPE for
graphs, change the view window to H-VIEW: 0 32, V-VIEW: -10 10, and
BarWidth to 1. Press
@CANCL $ to return to normal calculator display.
To perform the FFT on the array in stack level 1 use function FFT available in the
MTH/FFT menu on array
ΣDAT: @£DAT FFT. The FFT returns an array of complex
numbers that are the arrays of coefficients X
k
of the DFT. The magnitude of the
coefficients X
k
represents a frequency spectrum of the original data. To obtain
the magnitude of the coefficients you could transform the array into a list, and
then apply function ABS to the list. This is accomplished by using: OBJ
μ
ƒ LIST „Ê
Finally, you can convert the list back to a column vector to be stored in ΣDAT, as
follows: OBJ 1 ` 2 LIST ARRY STOΣ
To plot the spectrum, follow the instructions for producing a bar plot given
earlier. The vertical range needs to be changed to –1 to 80. The spectrum of
frequencies is the following:
The spectrum shows two large components for two frequencies (these are the
sinusoidal components, sin (3x) and cos(5x)), and a number of smaller
components for other frequencies.