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The SPECTRA Procedure |

If the number of observations *n* factors into prime
integers that are less than or equal to 23, and the
product of the square-free factors of *n* is less than 210,
then PROC SPECTRA uses the Fast Fourier Transform
developed by Cooley and Tukey and implemented by Singleton (1969).
If *n* cannot be factored in this way,
then PROC SPECTRA uses a Chirp-Z algorithm similar to that proposed by
Monro and Branch (1976).
To reduce memory requirements, when *n* is small
the Fourier coefficients are computed directly using the defining formulas.

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