# HP 48gII User Manual Page 529

Graphing calculator.

in the command catalog, ‚N). Store the array into variable ΣDAT by
using function STOΣ (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
of the DFT. The
k
magnitude of the coefficients X
represents a frequency spectrum of the
k
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
µ ƒ
LIST „Ê
accomplished by using: OBJ
Finally, you can convert the list back to a column vector to be stored in ΣDAT,
1 ` 2
as follows:
OBJ
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.
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