Optimize average2: replace array expression with explicit loops

(cherry picked from commit 1dc622e516)

AMSS_NCKU_source/fmisc.f90

@@ -1830,8 +1830,15 @@ deallocate(f_flat)
 ! f=3/8*f_1 + 3/4*f_2 - 1/8*f_3
 
   real*8,parameter::C1=3.d0/8.d0,C2=3.d0/4.d0,C3=-1.d0/8.d0
+  integer :: i,j,k
 
-  fout = C1*f1+C2*f2+C3*f3
+  do k=1,ext(3)
+   do j=1,ext(2)
+    do i=1,ext(1)
+      fout(i,j,k) = C1*f1(i,j,k)+C2*f2(i,j,k)+C3*f3(i,j,k)
+    enddo
+   enddo
+  enddo
 
   return