Fast Fourier transform: Difference between revisions

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 =={{header|J}}==
+Based on [[j:Essays/FFT]], with some simplifications, sacrificing accuracy not visible here for clarity:
-From [[j:Essays/FFT]]:
-<lang j>cube  =: ($~ q:@#) :. ,
+<lang j>cube  =: $~ q:@#
-roots =: +@]^:(0>[)  (_1^2%]) ^ i.@-:   NB. The elegant version, but less accurate
+roots =: +@]^:(0>[)  (_1^2%]) ^ i.@-:
-rou   =: [: (, j.) [: (, (j.~%:0.5) , |."1&.:+.@|.@}.) [: ^@o.@:j. i.@(%&8) % -:   NB. roots of unity
+rou   =: [: j./ 2 1 o./ o.@(% #)@i.@-:
 floop =: 4 : 'for_r. i.#$x do. (y=.{."1 y) ] x=.(+/x) ,&,:"r (-/x)*y end.'
 fft   =: (     ] floop&.cube   rou@#) f. :. ifft