subroutine xcor4(s2,ipk,nsteps,nsym,lag1,lag2,ich,mode4,ccf,ccf0, & lagpk,flip) ! Computes ccf of the 4_FSK spectral array s2 and the pseudo-random ! array pr2. Returns peak of CCF and the lag at which peak occurs. ! The CCF peak may be either positive or negative, with negative ! implying the "OOO" message. parameter (NHMAX=1260) !Max length of power spectra parameter (NSMAX=525) !Max number of half-symbol steps real s2(NHMAX,NSMAX) !2d spectrum, stepped by half-symbols real a(NSMAX) real ccf(-5:540) integer nch(7) integer npr2(207) real pr2(207) logical first data lagmin/0/ !Silence compiler warning data first/.true./ data npr2/ & 0,0,0,0,1,1,0,0,0,1,1,0,1,1,0,0,1,0,1,0,0,0,0,0,0,0,1,1,0,0, & 0,0,0,0,0,0,0,0,0,0,1,0,1,1,0,1,1,0,1,0,1,1,1,1,1,0,1,0,0,0, & 1,0,0,1,0,0,1,1,1,1,1,0,0,0,1,0,1,0,0,0,1,1,1,1,0,1,1,0,0,1, & 0,0,0,1,1,0,1,0,1,0,1,0,1,0,1,1,1,1,1,0,1,0,1,0,1,1,0,1,0,1, & 0,1,1,1,0,0,1,0,1,1,0,1,1,1,1,0,0,0,0,1,1,0,1,1,0,0,0,1,1,1, & 0,1,1,1,0,1,1,1,0,0,1,0,0,0,1,1,0,1,1,0,0,1,0,0,0,1,1,1,1,1, & 1,0,0,1,1,0,0,0,0,1,1,0,0,0,1,0,1,1,0,1,1,1,1,0,1,0,1/ data nch/1,2,4,9,18,36,72/ save if(first) then do i=1,207 pr2(i)=2*npr2(i)-1 enddo first=.false. endif ccfmax=0. ccfmin=0. nw=nch(ich) do j=1,nsteps n=2*mode4 if(mode4.eq.1) then a(j)=max(s2(ipk+n,j),s2(ipk+3*n,j)) - max(s2(ipk ,j),s2(ipk+2*n,j)) else kz=max(1,nw/2) ss0=0. ss1=0. ss2=0. ss3=0. wsum=0. do k=-kz+1,kz-1 w=float(kz-iabs(k))/nw wsum=wsum+w ss0=ss0 + w*s2(ipk +k,j) ss1=ss1 + w*s2(ipk+ n+k,j) ss2=ss2 + w*s2(ipk+2*n+k,j) ss3=ss3 + w*s2(ipk+3*n+k,j) enddo a(j)=(max(ss1,ss3) - max(ss0,ss2))/sqrt(wsum) endif enddo do lag=lag1,lag2 x=0. do i=1,nsym j=2*i-1+lag if(j.ge.1 .and. j.le.nsteps) x=x+a(j)*pr2(i) enddo ccf(lag)=2*x !The 2 is for plotting scale if(ccf(lag).gt.ccfmax) then ccfmax=ccf(lag) lagpk=lag endif if(ccf(lag).lt.ccfmin) then ccfmin=ccf(lag) lagmin=lag endif enddo ccf0=ccfmax flip=1.0 if(-ccfmin.gt.ccfmax) then do lag=lag1,lag2 ccf(lag)=-ccf(lag) enddo lagpk=lagmin ccf0=-ccfmin flip=-1.0 endif return end subroutine xcor4