Hp 48g Graphing Calculator Manual do Utilizador descarregar pdf (Página 164)

100

101

To prepare an array for fast Fourier transforms:

1. Put the array of data on the stack.

2. If necessary, add zeros to the array so that all dimensions are equal

to an integral power of two. See chapter 14 for efficient ways to add

columns or rows of zeros to matrices.

To use a fast Fourier transform:

1. Enter the array of data to be transformed (or its name) onto

the stack. Make sure its dimensions are integral powers of 2 (see

above).

2. Press fMTH 1 (NXT 1 FFT FFT to transform the data from the

time domain to the frequency domain.

Press (i/ffFn fNXT) FFT I FFT to transform the data from the

frequency domain to the time domain.

Example: Using FFT and IFFT for forward and inverse fast Fourier

transforms. The example uses the elements of a random

vector to represent a sampled signal.

1. Create a 16-eIement random vector on the stack: enter -C16> RflNM.

2. Compute the one-dimensional discrete Fourier transform of this

signal: execute FFT. The elements of the resulting vector represent

the frequency components of the original signal.

3. Reconstruct the original signal by computing the one-dimensional

inverse discrete Fourier transform: execute IFFT. The result is the

same as the original signal, subject to small rounding errors.

You can compute two-dimensional Fourier transforms using matrices

as arguments. For instance, use a random 16x16 matrix in the above

example: {16 16> RFiNM.

13-8 Vectors and Transforms

1 2 ... 159 160 161 162 163 164 165 166 167 168 169 ... 611 612

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