Merge pull request #58 from fverdugo/francesc

More changes in jacobi_notebook

docs/src/solutions_for_all_notebooks.md

@@ -292,72 +292,108 @@ end
 
 ```julia
 function jacobi_mpi(n,niters)
-    comm = MPI.COMM_WORLD
-    nranks = MPI.Comm_size(comm)
+    u, u_new = init(n,comm)
+    load = length(u)-2
     rank = MPI.Comm_rank(comm)
-    if mod(n,nranks) != 0
-        println("n must be a multiple of nranks")
-        MPI.Abort(comm,1)
-    end
-    load = div(n,nranks)
-    u = zeros(load+2)
-    u[1] = -1
-    u[end] = 1
-    u_new = copy(u)
+    nranks = MPI.Comm_size(comm)
+    nreqs = 2*((rank != 0) + (rank != (nranks-1)))
+    reqs = MPI.MultiRequest(nreqs)
     for t in 1:niters
-        reqs = MPI.Request[]
+        ireq = 0
         if rank != 0
             neig_rank = rank-1
-            req = MPI.Isend(view(u,2:2),comm,dest=neig_rank,tag=0)
-            push!(reqs,req)
-            req = MPI.Irecv!(view(u,1:1),comm,source=neig_rank,tag=0)
-            push!(reqs,req)
+            u_snd = view(u,2:2)
+            u_rcv = view(u,1:1)
+            dest = neig_rank
+            source = neig_rank
+            ireq += 1
+            MPI.Isend(u_snd,comm,reqs[ireq];dest)
+            ireq += 1
+            MPI.Irecv!(u_rcv,comm,reqs[ireq];source)
         end
         if rank != (nranks-1)
             neig_rank = rank+1
-            s = load+1
-            r = load+2
-            req = MPI.Isend(view(u,s:s),comm,dest=neig_rank,tag=0)
-            push!(reqs,req)
-            req = MPI.Irecv!(view(u,r:r),comm,source=neig_rank,tag=0)
-            push!(reqs,req)
+            u_snd = view(u,(load+1):(load+1))
+            u_rcv = view(u,(load+2):(load+2))
+            dest = neig_rank
+            source = neig_rank
+            ireq += 1
+            MPI.Isend(u_snd,comm,reqs[ireq];dest)
+            ireq += 1
+            MPI.Irecv!(u_rcv,comm,reqs[ireq];source)
         end
+        # Upload interior cells
         for i in 3:load
             u_new[i] = 0.5*(u[i-1]+u[i+1])
         end
+        # Wait for the communications to finish
         MPI.Waitall(reqs)
+        # Update boundaries
         for i in (2,load+1)
             u_new[i] = 0.5*(u[i-1]+u[i+1])
         end
         u, u_new = u_new, u
-
     end
-    # Gather the results
-    if rank !=0
-        lb = 2
-        ub = load+1
-        MPI.Send(view(u,lb:ub),comm,dest=0)
-        u_all = zeros(0) # This will nevel be used
-    else
-        u_all = zeros(n+2)
-        # Set boundary
-        u_all[1] = -1
-        u_all[end] = 1
-        # Set data for rank 0
-        lb = 2
-        ub = load+1
-        u_all[lb:ub] = view(u,lb:ub)
-        # Set data for other ranks
-        for other_rank in 1:(nranks-1)
-            lb += load
-            ub += load
-            MPI.Recv!(view(u_all,lb:ub),comm;source=other_rank)
+    return u
+end
+```
+
+### Exercise 2
+
+```julia
+function jacobi_mpi(n,niters,tol,comm) # new tol arg
+    u, u_new = init(n,comm)
+    load = length(u)-2
+    rank = MPI.Comm_rank(comm)
+    nranks = MPI.Comm_size(comm)
+    nreqs = 2*((rank != 0) + (rank != (nranks-1)))
+    reqs = MPI.MultiRequest(nreqs)
+    for t in 1:niters
+        ireq = 0
+        if rank != 0
+            neig_rank = rank-1
+            u_snd = view(u,2:2)
+            u_rcv = view(u,1:1)
+            dest = neig_rank
+            source = neig_rank
+            ireq += 1
+            MPI.Isend(u_snd,comm,reqs[ireq];dest)
+            ireq += 1
+            MPI.Irecv!(u_rcv,comm,reqs[ireq];source)
+        end
+        if rank != (nranks-1)
+            neig_rank = rank+1
+            u_snd = view(u,(load+1):(load+1))
+            u_rcv = view(u,(load+2):(load+2))
+            dest = neig_rank
+            source = neig_rank
+            ireq += 1
+            MPI.Isend(u_snd,comm,reqs[ireq];dest)
+            ireq += 1
+            MPI.Irecv!(u_rcv,comm,reqs[ireq];source)
         end
+        MPI.Waitall(reqs)
+        # Compute the max diff in the current
+        # rank while doing the local update
+        mydiff = 0.0
+        for i in 2:load+1
+            u_new[i] = 0.5*(u[i-1]+u[i+1])
+            diff_i = abs(u_new[i] - u[i])
+            mydiff = max(mydiff,diff_i)
+        end
+        # Now we need to find the global diff
+        diff_ref = Ref(mydiff)
+        MPI.Allreduce!(diff_ref,max,comm)
+        diff = diff_ref[]
+        # If global diff below tol, stop!
+        if diff < tol
+            return u_new
+        end
+        u, u_new = u_new, u
     end
-    return u_all
+    return u
 end
 ```
 
 
 
-

notebooks/jacobi_method.ipynb

@@ -281,7 +281,7 @@
    "outputs": [],
    "source": [
     "n = 5\n",
-    "tol = 1e-9\n",
+    "tol = 1e-10\n",
     "jacobi_with_tol(n,tol)"
    ]
   },
@@ -1531,7 +1531,7 @@
     "    u = jacobi_mpi(n,niters,comm)\n",
     "    @show u\n",
     "end\n",
-    "run(`$(mpiexec()) -np 1 julia --project=. -e $code`);"
+    "run(`$(mpiexec()) -np 3 julia --project=. -e $code`);"
    ]
   },
   {
@@ -1914,7 +1914,7 @@
    "source": [
     "### Exercise 2\n",
     "\n",
-    "In the parallel implementation of the Jacobi method, we assumed that the method runs for a given number of iterations. In function, `jacobi_with_tol` at the beginning of the notebook shows how the Jacobi iterations can be stopped when the difference between iterations is small. Implement a parallel version of this function. Start with the in Exercise 1 and add the stopping criterion implemented in `jacobi_with_tol`. Use a text editor and the Julia REPL. Do not try to implement the code in a notebook."
+    "In the parallel implementation of the Jacobi method, we assumed that the method runs for a given number of iterations. In function, `jacobi_with_tol` at the beginning of the notebook shows how the Jacobi iterations can be stopped when the difference between iterations is small. Implement a parallel version of this function. Start with the code in Exercise 1 and add the stopping criterion implemented in `jacobi_with_tol`. Use a text editor and the Julia REPL. Do not try to implement the code in a notebook."
    ]
   },
   {

notebooks/pdes.ipynb

@@ -1534,15 +1534,15 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Julia 1.9.1",
+   "display_name": "Julia 1.9.0",
    "language": "julia",
    "name": "julia-1.9"
   },
   "language_info": {
    "file_extension": ".jl",
    "mimetype": "application/julia",
    "name": "julia",
-   "version": "1.9.1"
+   "version": "1.9.0"
   }
  },
  "nbformat": 4,