ice_dyn_vp: use 'global_sum_prod' for bit-for-bit log reproducibility

In the previous commits we ensured bit-for-bit reproducibility of the
outputs when using the VP solver.

Some global norms computed during the nonlinear iteration still use the
same non-reproducible pattern of summing over blocks locally before
performing the reduction. However, these norms are used only to monitor
the convergence in the log file, as well as to exit the iteration when
the required convergence level is reached ('nlres_norm'). Only
'nlres_norm' could (in theory) influence the output, but it is unlikely
that a difference due to floating point errors would influence the 'if
(nlres_norm < tol_nl)' condition used to exist the nonlinear iteration.

Change these remaining cases to also use 'global_sum_prod' to compute
the global norm, leading to bit-for-bit log reproducibility.

cicecore/cicedynB/dynamics/ice_dyn_vp.F90

@@ -901,7 +901,8 @@ subroutine anderson_solver (icellt  , icellu , &
                                L2norm       (iblk))
          enddo
          !$OMP END PARALLEL DO
-         nlres_norm = sqrt(global_sum(sum(L2norm), distrb_info))
+         nlres_norm = sqrt(global_sum_prod(Fx(:,:,:), Fx(:,:,:), distrb_info, field_loc_NEcorner) + &
+                           global_sum_prod(Fy(:,:,:), Fy(:,:,:), distrb_info, field_loc_NEcorner))
          if (my_task == master_task .and. monitor_nonlin) then
             write(nu_diag, '(a,i4,a,d26.16)') "monitor_nonlin: iter_nonlin= ", it_nl, &
                                               " nonlin_res_L2norm= ", nlres_norm
@@ -991,16 +992,8 @@ subroutine anderson_solver (icellt  , icellu , &
                              indxui   (:,:), indxuj(:,:) , &
                              res        (:),               &
                              fpresx (:,:,:), fpresy (:,:,:))
-         !$OMP PARALLEL DO PRIVATE(iblk)
-         do iblk = 1, nblocks
-            call calc_L2norm_squared (nx_block        , ny_block        , &
-                                      icellu    (iblk),                   &
-                                      indxui  (:,iblk), indxuj  (:,iblk), &
-                                      fpresx(:,:,iblk), fpresy(:,:,iblk), &
-                                      L2norm    (iblk))
-         enddo
-         !$OMP END PARALLEL DO
-         fpres_norm = sqrt(global_sum(sum(L2norm), distrb_info))
+         fpres_norm = sqrt(global_sum_prod(fpresx(:,:,:), fpresx(:,:,:), distrb_info, field_loc_NEcorner) + &
+                           global_sum_prod(fpresy(:,:,:), fpresy(:,:,:), distrb_info, field_loc_NEcorner))
 #endif
          if (my_task == master_task .and. monitor_nonlin) then
             write(nu_diag, '(a,i4,a,d26.16)') "monitor_nonlin: iter_nonlin= ", it_nl, &
@@ -1128,14 +1121,10 @@ subroutine anderson_solver (icellt  , icellu , &
          do iblk = 1, nblocks
             fpresx(:,:,iblk) = uvel(:,:,iblk) - uprev_k(:,:,iblk)
             fpresy(:,:,iblk) = vvel(:,:,iblk) - vprev_k(:,:,iblk)
-            call calc_L2norm_squared (nx_block        , ny_block        , &
-                                      icellu    (iblk),                   &
-                                      indxui  (:,iblk), indxuj  (:,iblk), &
-                                      fpresx(:,:,iblk), fpresy(:,:,iblk), &
-                                      L2norm    (iblk))
          enddo
          !$OMP END PARALLEL DO
-         prog_norm = sqrt(global_sum(sum(L2norm), distrb_info))
+         prog_norm = sqrt(global_sum_prod(fpresx(:,:,:), fpresx(:,:,:), distrb_info, field_loc_NEcorner) + &
+                          global_sum_prod(fpresy(:,:,:), fpresy(:,:,:), distrb_info, field_loc_NEcorner))
          if (my_task == master_task .and. monitor_nonlin) then
             write(nu_diag, '(a,i4,a,d26.16)') "monitor_nonlin: iter_nonlin= ", it_nl, &
                                               " progress_res_L2norm= ", prog_norm