77 lines
2.1 KiB
Plaintext
77 lines
2.1 KiB
Plaintext
program t3
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parameter (NBLK=3456,NZ=10*NBLK)
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real x0(NZ)
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real x1(NZ)
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twopi=8.0*atan(1.0)
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dphi=twopi*1000.0/12000.0
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phi=0.
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do i=1,NZ
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phi=phi+dphi
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x0(i)=sin(phi)
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if(mod(i,10007).eq.100) x0(i)=2.0
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enddo
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do j=1,10
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ib=j*NBLK
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ia=ib-NBLK+1
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call filter(x0(ia:ib),x1(ia:ib))
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enddo
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x1(1:NZ-NBLK)=x1(NBLK+1:NZ)
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do i=1,NZ-NBLK
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write(13,1001) i,x0(i),x1(i),x1(i)-x0(i)
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1001 format(i6,3f13.9)
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enddo
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end program t3
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subroutine filter(x0,x1)
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! Process time-domain data sequentially, optionally using a frequency-domain
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! filter to alter the spectrum.
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! NB: uses a sin^2 window with 50% overlap.
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parameter (NFFT=6912,NH=NFFT/2)
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real x0(0:NH-1) !Input samples
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real x1(0:NH-1) !Output samples (delayed by one block)
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real x0s(0:NH-1) !Saved upper half of input samples
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real x1s(0:NH-1) !Saved upper half of output samples
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real x(0:NFFT-1) !Work array
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real*4 w(0:NFFT-1) !Window function
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real f(0:NH) !Filter to be applied
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real*4 s(0:NH) !Average spectrum
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logical first
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complex cx(0:NH) !Complex frequency-domain work array
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equivalence (x,cx)
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data first/.true./
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save
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if(first) then
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pi=4.0*atan(1.0)
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do i=0,NFFT-1
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ww=sin(i*pi/NFFT)
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w(i)=ww*ww/NFFT
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enddo
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s=0.0
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f=1.0
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x0s=0.
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x1s=0.
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first=.false.
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endif
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x(0:NH-1)=x0s !Previous 2nd half to new 1st half
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x(NH:NFFT-1)=x0 !New 2nd half
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x0s=x0 !Save the new 2nd half
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x=w*x !Apply window
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call four2a(x,NFFT,1,-1,0) !r2c FFT (to frequency domain)
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cx=f*cx
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call four2a(cx,NFFT,1,1,-1) !c2r FFT (back to time domain)
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x1=x1s + x(0:NH-1) !Add previous segment's 2nd half
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x1s=x(NH:NFFT-1) !Save the new 2nd half
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return
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end subroutine filter
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