2005-12-22 16:40:53 +00:00
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subroutine xcor(s2,ipk,nsteps,nsym,lag1,lag2,
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+ ccf,ccf0,lagpk,flip,fdot)
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C Computes ccf of a row of s2 and the pseudo-random array pr. Returns
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C peak of the CCF and the lag at which peak occurs. For JT65, the
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C CCF peak may be either positive or negative, with negative implying
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C the "OOO" message.
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parameter (NHMAX=1024) !Max length of power spectra
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parameter (NSMAX=320) !Max number of half-symbol steps
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real s2(NHMAX,NSMAX) !2d spectrum, stepped by half-symbols
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real a(NSMAX),a2(NSMAX)
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2006-01-12 22:10:21 +00:00
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real ccf(-5:540)
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2005-12-22 16:40:53 +00:00
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include 'prcom.h'
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common/clipcom/ nclip
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data lagmin/0/ !Silence g77 warning
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save
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df=11025.0/4096.
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dtstep=0.5/df
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fac=dtstep/(60.0*df)
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do j=1,nsteps
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ii=nint((j-nsteps/2)*fdot*fac)+ipk
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a(j)=s2(ii,j)
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enddo
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C If requested, clip the spectrum that will be cross correlated.
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nclip=0 !Turn it off
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if(nclip.gt.0) then
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call pctile(a,a2,nsteps,50,base)
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alow=a2(nint(nsteps*0.16))
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ahigh=a2(nint(nsteps*0.84))
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rms=min(base-alow,ahigh-base)
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clip=4.0-nclip
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atop=base+clip*rms
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abot=base-clip*rms
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do i=1,nsteps
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if(nclip.lt.4) then
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a(i)=min(a(i),atop)
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a(i)=max(a(i),abot)
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else
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if(a(i).ge.base) then
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a(i)=1.0
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else
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a(i)=-1.0
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endif
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endif
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enddo
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endif
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ccfmax=0.
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ccfmin=0.
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do lag=lag1,lag2
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x=0.
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do i=1,nsym
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j=2*i-1+lag
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if(j.ge.1 .and. j.le.nsteps) x=x+a(j)*pr(i)
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enddo
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ccf(lag)=2*x !The 2 is for plotting scale
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if(ccf(lag).gt.ccfmax) then
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ccfmax=ccf(lag)
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lagpk=lag
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endif
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if(ccf(lag).lt.ccfmin) then
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ccfmin=ccf(lag)
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lagmin=lag
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endif
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enddo
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ccf0=ccfmax
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flip=1.0
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if(-ccfmin.gt.ccfmax) then
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do lag=lag1,lag2
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ccf(lag)=-ccf(lag)
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enddo
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lagpk=lagmin
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ccf0=-ccfmin
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flip=-1.0
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endif
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return
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end
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