HP 48gII hp 48gII_user's manual_English_E_HDPMSG48E67_V2.pdf - Page 529

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 Xk of the DFT. The magnitude of the coefficients Xk 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. Page 16-51