fit.f90

FORTRANvisualfortran常用数值算法集及源码

SUBROUTINE fit(x,y,ndata,sig,mwt,a,b,siga,sigb,chi2,q)
INTEGER mwt,ndata
REAL a,b,chi2,q,siga,sigb,sig(ndata),x(ndata),y(ndata)
!USES gammq
INTEGER i
REAL sigdat,ss,st2,sx,sxoss,sy,t,wt,gammq
sx=0.
sy=0.
st2=0.
b=0.
if(mwt/=0) then
  ss=0.
  do i=1,ndata
    wt=1./(sig(i)**2)
    ss=ss+wt
    sx=sx+x(i)*wt
    sy=sy+y(i)*wt
  end do
else
  do i=1,ndata
    sx=sx+x(i)
    sy=sy+y(i)
  end do
  ss=float(ndata)
endif
sxoss=sx/ss
if(mwt/=0) then
  do i=1,ndata
    t=(x(i)-sxoss)/sig(i)
    st2=st2+t*t
    b=b+t*y(i)/sig(i)
  end do
else
  do i=1,ndata
    t=x(i)-sxoss
    st2=st2+t*t
    b=b+t*y(i)
  end do
endif
b=b/st2
a=(sy-sx*b)/ss
siga=sqrt((1.+sx*sx/(ss*st2))/ss)
sigb=sqrt(1./st2)
chi2=0.
if(mwt==0) then
  do i=1,ndata
    chi2=chi2+(y(i)-a-b*x(i))**2
  end do
  q=1.
  sigdat=sqrt(chi2/(ndata-2))
  siga=siga*sigdat
  sigb=sigb*sigdat
else
  do i=1,ndata
    chi2=chi2+((y(i)-a-b*x(i))/sig(i))**2
  end do
  q=gammq(0.5*(ndata-2),0.5*chi2)
endif
END SUBROUTINE fit