Added solutions for Jacobi notebook

docs/src/solutions_for_all_notebooks.md

@@ -213,4 +213,58 @@ end
 
 At each call to @spawnat we will communicate O(N) and compute O(N) in a worker process just like in algorithm 1. However, we will do this work N^2/P times on average at each worker. Thus, the total communication and computation on a worker will be O(N^3/P) for both communication and computation.  Thus, the communication over computation ratio will still be O(1) and thus the communication will dominate in practice, making the algorithm inefficient.
 
+## Jacobi method
+
+### Exercise 1
+
+```julia
+@everywhere workers() begin
+    using MPI
+    comm = MPI.Comm_dup(MPI.COMM_WORLD)
+    function jacobi_mpi(n,niters)
+        nranks = MPI.Comm_size(comm)
+        rank = MPI.Comm_rank(comm)
+        if mod(n,nranks) != 0
+            println("n must be a multiple of nranks")
+            MPI.Abort(comm,1)
+        end
+        n_own = div(n,nranks)
+        u = zeros(n_own+2)
+        u[1] = -1
+        u[end] = 1
+        u_new = copy(u)
+        for t in 1:niters
+            reqs = MPI.Request[]
+            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)
+            end
+            if rank != (nranks-1)
+                neig_rank = rank+1
+                s = n_own+1
+                r = n_own+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)
+            end
+            for i in 3:n_own
+                u_new[i] = 0.5*(u[i-1]+u[i+1])
+            end
+            MPI.Waitall(reqs)
+            for i in (2,n_own+1)
+                u_new[i] = 0.5*(u[i-1]+u[i+1])
+            end
+            u, u_new = u_new, u
+        end
+        return u
+    end
+end
+```
+
+
+