2015-04-22 17:48:03 +00:00
|
|
|
subroutine polyfit(x,y,sigmay,npts,nterms,mode,a,chisqr)
|
2014-01-08 18:38:15 +00:00
|
|
|
implicit real*8 (a-h,o-z)
|
|
|
|
|
real*8 x(npts), y(npts), sigmay(npts), a(nterms)
|
2016-11-30 00:40:50 +00:00
|
|
|
real*8 sumx(10), sumy(10), array(10,10)
|
2014-01-08 18:38:15 +00:00
|
|
|
|
|
|
|
|
! Accumulate weighted sums
|
|
|
|
|
nmax = 2*nterms-1
|
|
|
|
|
sumx=0.
|
|
|
|
|
sumy=0.
|
|
|
|
|
chisq=0.
|
|
|
|
|
do i=1,npts
|
|
|
|
|
xi=x(i)
|
|
|
|
|
yi=y(i)
|
|
|
|
|
if(mode.lt.0) then
|
|
|
|
|
weight=1./abs(yi)
|
|
|
|
|
else if(mode.eq.0) then
|
|
|
|
|
weight=1
|
|
|
|
|
else
|
|
|
|
|
weight=1./sigmay(i)**2
|
|
|
|
|
end if
|
|
|
|
|
xterm=weight
|
|
|
|
|
do n=1,nmax
|
|
|
|
|
sumx(n)=sumx(n)+xterm
|
|
|
|
|
xterm=xterm*xi
|
|
|
|
|
enddo
|
|
|
|
|
yterm=weight*yi
|
|
|
|
|
do n=1,nterms
|
|
|
|
|
sumy(n)=sumy(n)+yterm
|
|
|
|
|
yterm=yterm*xi
|
|
|
|
|
enddo
|
|
|
|
|
chisq=chisq+weight*yi**2
|
|
|
|
|
enddo
|
|
|
|
|
|
|
|
|
|
! Construct matrices and calculate coefficients
|
|
|
|
|
do j=1,nterms
|
|
|
|
|
do k=1,nterms
|
|
|
|
|
n=j+k-1
|
|
|
|
|
array(j,k)=sumx(n)
|
|
|
|
|
enddo
|
|
|
|
|
enddo
|
|
|
|
|
|
|
|
|
|
delta=determ(array,nterms)
|
|
|
|
|
if(delta.eq.0) then
|
|
|
|
|
chisqr=0.
|
|
|
|
|
a=0.
|
|
|
|
|
else
|
|
|
|
|
do l=1,nterms
|
|
|
|
|
do j=1,nterms
|
|
|
|
|
do k=1,nterms
|
|
|
|
|
n=j+k-1
|
|
|
|
|
array(j,k)=sumx(n)
|
|
|
|
|
enddo
|
|
|
|
|
array(j,l)=sumy(j)
|
|
|
|
|
enddo
|
|
|
|
|
a(l)=determ(array,nterms)/delta
|
|
|
|
|
enddo
|
|
|
|
|
|
|
|
|
|
! Calculate chi square
|
|
|
|
|
|
|
|
|
|
do j=1,nterms
|
|
|
|
|
chisq=chisq-2*a(j)*sumy(j)
|
|
|
|
|
do k=1,nterms
|
|
|
|
|
n=j+k-1
|
|
|
|
|
chisq=chisq+a(j)*a(k)*sumx(n)
|
|
|
|
|
enddo
|
|
|
|
|
enddo
|
|
|
|
|
free=npts-nterms
|
|
|
|
|
chisqr=chisq/free
|
|
|
|
|
end if
|
|
|
|
|
|
|
|
|
|
return
|
2015-04-22 17:48:03 +00:00
|
|
|
end subroutine polyfit
|
