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subroutine correl
c******************************************************************************
c This routine cross-correlates arrays x and y using any part of the
c arrays, as long as there are enough data points in each array.
c The result is printed out in terms of the shift in the abscissa
c of the y array needed to align it with the x array.
c******************************************************************************
include 'Atmos.com'
include 'Linex.com'
include 'Pstuff.com'
include 'Equivs.com'
include 'Plotval.com'
real*4 xgood(100000), ygood(100000), zgood(100000)
real*8 spx(1000), spy(1000)
real*4 q
real*8 xinterp(21), yinterp(21)
wavemin = amax1(xsyn(1),xobs(1))
wavemax = amin1(xsyn(kount),xobs(lount))
wavecenter = (wavemax + wavemin)/2.
c*****find the array subscripts for the minimum and maximum
c wavelengths in the synthetic spectrum.
do i=1,kount
if (xsyn(i) >= wavemin) then
ilosyn = i
go to 5
endif
enddo
5 do i=ilosyn,kount
if (xsyn(i) > wavemax) then
ihisyn = i - 1
go to 10
endif
enddo
ihisyn = kount
c*****dump the synthetic spectrum wavelengths and fluxes into working arrays
10 itotsyn = ihisyn - ilosyn + 1
do i=1, itotsyn
xgood(i) = xsyn(ilosyn-1+i)
ygood(i) = chunk(ilosyn-1+i,1)
enddo
c*****find the array subscript for the minimum wavelength in the
c observed spectrum
do j=1,lount
if (xobs(j) >= xgood(1)) then
jloobs = j
go to 15
endif
enddo
c*****using a 3-point Lagrangian, make an interpolated observed
c spectrum that matches the wavelength step size of the
c synthetic spectrum
15 j = jloobs
do i=1,itotsyn
if (xgood(i) > (xobs(j+1)+xobs(j))/2.) j = j + 1
q = xgood(i)
zgood(i) = yobs(j-1)*(q-xobs(j))*(q-xobs(j+1))/
. ((xobs(j-1)-xobs(j))*(xobs(j-1)-xobs(j+1))) +
. yobs(j)*(q-xobs(j-1))*(q-xobs(j+1))/
. ((xobs(j)-xobs(j-1))*(xobs(j)-xobs(j+1))) +
. yobs(j+1)*(q-xobs(j-1))*(q-xobs(j))/
. ((xobs(j+1)-xobs(j-1))*(xobs(j+1)-xobs(j)))
enddo
c*****next, EITHER do a single cross-correlation
call crosscorr (ishift,spy(1),ygood,zgood,itotsyn)
c*****next, do the cross-correlation:
imax = 2*maxshift + 1
do i=1,imax
ishift = i - 1 - maxshift
spx(i) = dble(ishift)
call crosscorr (ishift,spy(i),ygood,zgood,itotsyn)
enddo
c*****interpolate to find the maximum of the correlation function
corrmax = spy(1)
mc = 1
do i=2,imax
if (spy(i) > corrmax) then
corrmax = spy(i)
mc = i
endif
enddo
if (mc==1 .or. mc==imax) then
deltawave = 0.
return
endif
xinterp(1) = spx(mc-1)
yinterp(1) = spy(mc-1)
do j=2,21
q = spx(mc-1) + (j-1)/10.
xinterp(j) = q
yinterp(j) = spy(mc-1)*(q-spx(mc))*(q-spx(mc+1))/
. ((spx(mc-1)-spx(mc))*(spx(mc-1)-spx(mc+1))) +
. spy(mc)*(q-spx(mc-1))*(q-spx(mc+1))/
. ((spx(mc)-spx(mc-1))*(spx(mc)-spx(mc+1))) +
. spy(mc+1)*(q-spx(mc-1))*(q-spx(mc))/
. ((spx(mc+1)-spx(mc-1))*(spx(mc+1)-spx(mc)))
enddo
jmax = 1
corrmax = yinterp(1)
do j=2,21
if (yinterp(j) > corrmax) then
jmax = j
corrmax = yinterp(j)
shiftmax = xinterp(j)
endif
enddo
c*****translate this into a correction to the input velocity shift
deltawave = -step*shiftmax
deltavel = -3.0d5*step*shiftmax/wavecenter
veladd = veladd + deltavel
return
end
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