subroutine lorentzian(y,npts,a) ! Input: y(npts); assume x(i)=i, i=1,npts ! Output: a(4) ! a(1) = baseline ! a(2) = amplitude ! a(3) = x0 ! a(4) = width real y(npts) real a(5) real deltaa(4) if(npts.gt.2000) stop 'Error in lorentzian' a=0. df=12000.0/8192.0 !df = 1.465 Hz width=0. ipk=0 ymax=-1.e30 do i=1,npts if(y(i).gt.ymax) then ymax=y(i) ipk=i endif ! write(50,3001) i,i*df,y(i) !3001 format(i6,2f12.3) enddo ! base=(sum(y(ipk-149:ipk-50)) + sum(y(ipk+51:ipk+150)))/200.0 base=(sum(y(1:20)) + sum(y(npts-19:npts)))/40.0 stest=ymax - 0.5*(ymax-base) ssum=y(ipk) do i=1,50 if(ipk+i.gt.npts) exit if(y(ipk+i).lt.stest) exit ssum=ssum + y(ipk+i) enddo do i=1,50 if(ipk-i.lt.1) exit if(y(ipk-i).lt.stest) exit ssum=ssum + y(ipk-i) enddo ww=ssum/y(ipk) width=2 t=ww*ww - 5.67 if(t.gt.0.0) width=sqrt(t) a(1)=base a(2)=ymax-base a(3)=ipk a(4)=width ! Now find Lorentzian parameters deltaa(1)=0.1 deltaa(2)=0.1 deltaa(3)=1.0 deltaa(4)=1.0 nterms=4 ! Start the iteration chisqr=0. chisqr0=1.e6 do iter=1,5 do j=1,nterms chisq1=fchisq0(y,npts,a) fn=0. delta=deltaa(j) 10 a(j)=a(j)+delta chisq2=fchisq0(y,npts,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=fchisq0(y,npts,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,chisq2 !4000 format(i1,i2,4f10.4,f11.3) enddo chisqr=fchisq0(y,npts,a) ! write(*,4000) 0,0,a,chisqr if(chisqr/chisqr0.gt.0.99) exit chisqr0=chisqr enddo a(5)=chisqr return end subroutine lorentzian