WSJT-X/lib/afc9.f90

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subroutine afc9(c3,npts,fsample,a,syncpk)
complex c3(0:npts-1)
real a(3),deltaa(3)
a(1)=0. !f0
a(2)=0. !f1
a(3)=0. !f2
deltaa(1)=0.2
deltaa(2)=0.01
deltaa(3)=0.01
nterms=3
! Start the iteration
chisqr=0.
chisqr0=1.e6
do iter=1,4 !One iteration is enough?
do j=1,nterms
chisq1=fchisq(c3,npts,fsample,a)
fn=0.
delta=deltaa(j)
10 a(j)=a(j)+delta
chisq2=fchisq(c3,npts,fsample,a)
if(chisq2.eq.chisq1) go to 10
if(chisq2.gt.chisq1) then
delta=-delta !Reverse direction
a(j)=a(j)+delta
tmp=chisq1
chisq1=chisq2
chisq2=tmp
endif
20 fn=fn+1.0
a(j)=a(j)+delta
chisq3=fchisq(c3,npts,fsample,a)
if(chisq3.lt.chisq2) then
chisq1=chisq2
chisq2=chisq3
go to 20
endif
! Find minimum of parabola defined by last three points
delta=delta*(1./(1.+(chisq1-chisq2)/(chisq3-chisq2))+0.5)
a(j)=a(j)-delta
deltaa(j)=deltaa(j)*fn/3.
! write(*,4000) iter,j,a,deltaa,-chisq2
!4000 format(i1,i2,6f10.4,f9.3)
enddo
chisqr=fchisq(c3,npts,fsample,a)
if(chisqr/chisqr0.gt.0.9999) exit
chisqr0=chisqr
enddo
syncpk=-chisqr
! write(*,4001) a,deltaa,-chisq2
!4001 format(3x,6f10.4,f9.3)
return
end subroutine afc9