Fast Fourier transform: Difference between revisions
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contains |
contains |
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! In place Cooley-Tookey FFT |
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recursive subroutine fft(x) |
recursive subroutine fft(x) |
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complex(kind=dp), dimension(:), intent(inout) :: x |
complex(kind=dp), dimension(:), intent(inout) :: x |
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allocate(even((N+1)/2)) |
allocate(even((N+1)/2)) |
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! divide |
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odd=x(1:N:2) |
odd=x(1:N:2) |
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even=x(2:N:2) |
even=x(2:N:2) |
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! conquer |
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call fft(odd) |
call fft(odd) |
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call fft(even) |
call fft(even) |
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! combine |
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do i=1,N2 |
do i=1,N2 |
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t=exp(cmplx(0.0_dp,-2.0_dp*pi*real(i-1,dp)/real(N,dp)))*even(i) |
t=exp(cmplx(0.0_dp,-2.0_dp*pi*real(i-1,dp)/real(N,dp)))*even(i) |
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( 0.00, 0.00i ) |
( 0.00, 0.00i ) |
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( 1.00, 2.41i )</pre> |
( 1.00, 2.41i )</pre> |
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=={{header|GAP}}== |
=={{header|GAP}}== |
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