▼Math Library
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5.3.2
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10 Stuff That Doesn’t Belong Anywhere Else

Neil Toronto <ntoronto@racket-lang.org>

 (require math/utils)

parameter

(max-math-threads) → Positive-Integer

(max-math-threads num) → void?
  num : Positive-Integer
The maximum number of threads a parallelized math function will use. The default value is (max 1 (processor-count)).

parameter

(dft-convention) → (List Real Real)

(dft-convention lst) → void?
  lst : (List Real Real)
A parameter controlling the convention used for scaling discrete Fourier transforms, such as those performed by array-fft. The default value is '(1 -1), which represents the convention used in signal processing.

In general, if lst is (list a b) and n is the length of a transformed array axis or vector, then

  • Each sum is scaled by (expt n (/ (- a 1) 2)).

  • Each exponential in the sum has its argument scaled by b.

Conveniently, a Fourier transform with convention (list (- a) (- b)) is the inverse of a Fourier transform with convention (list a b).

See Mathematica’s documentation on Fourier, from which this excellent idea was stolen.

procedure

(dft-inverse-convention) → (List Real Real)

Returns the convention used for inverse Fourier transforms, given the current convention.

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