大家好，我最近写了一个计算相关函数的程序。按照归一化的相关函数的定义
A=(a(t)*a(0))/(a(0)*a(0))，我采用了两种平均的方法，第一种是先分别计算a(t)*a(0)的和以及a(0)*a(0)的和，然后结果相除。第二种是先计算a(t)*a(0))/(a(0)*a(0)，然后将所有的a(t)*a(0))/(a(0)*a(0)的求和，再平均，本想能得到相同的结果，可是两次输出的结果又很大区别。请大家帮忙看看是哪里出了问题。
我的程序是：
do i=1,10000 (粒子数)
     do ntel=1,npoints (共有npoints个数据)
          if (确定timeorigin的条件) then
             t0=t0+1
             time0(t0)=ntel
             A0(t0)=A(ntel)         
             do t=1,t0
                  delt=ntel-time0(t)+1
                  tcf(delt)=tcf(delt)+A(ntel)*A0(t)  
                  tcf0(delt)=tcf0(delt)+A0(t)*A0(t)
                  acf（delt）=acf(delt)+(A(ntel)*A0(t))/(A(t)*A0(t))    
             enddo
           endif
    enddo
enddo
do ical=1,npoints
WRITE(*,*) tcf(ical)=（tcf(ical)/nparticle*ntime(ical)/(tcf0(ical)&/nparticle*ntime(ical)
WRITE(*,*)  acf(ical)=acf(ical)/nparticle*ntime(ical)
enddo
可是输出的结果却又很大差别，下面是结果：
0.0000000000000000        1.0000000000000000     
   0.0000000000000000       1.14207400639561443E-004
   1.0000000149011612       0.67655786350148372     
   1.0000000149011612       7.72679149727596715E-005
   2.0000000298023224       0.62686567164179108     
   2.0000000298023224       7.15926989083817998E-005
   3.0000000447034836       0.60360360360360366     
   3.0000000447034836       6.89359985842397961E-005
   4.0000000596046448       0.58610271903323263     
   4.0000000596046448       6.69372680485647080E-005
   5.0000000745058060       0.57012195121951215     
   5.0000000745058060       6.51121460963353292E-005
   6.0000000894069672       0.55828220858895705     
   6.0000000894069672       6.37599598662582241E-005
   7.0000001043081284       0.54629629629629639     
   7.0000001043081284       6.23910799790196834E-005
   8.0000001192092896       0.51552795031055898     
   8.0000001192092896       5.88771071620099369E-005
   9.0000001341104507       0.52187499999999998     
   9.0000001341104507       5.96019872087711250E-005
   10.000000149011612       0.52515723270440251     
   10.000000149011612       5.99768424742350986E-005