Add gmg as the test case and fix bug in finding coarse levels

Author: ranjanan

src/classical.jl

@@ -20,7 +20,7 @@ function ruge_stuben{Ti,Tv}(A::SparseMatrixCSC{Ti,Tv};
 
     levels = Vector{Level{Ti,Tv}}()
 
-    while length(levels) + 1 < max_levels && size(A, 1) < max_coarse
+    while length(levels) + 1 < max_levels && size(A, 1) > max_coarse
         A = extend_heirarchy!(levels, strength, CF, A)
         #if size(A, 1) <= max_coarse
         #    break

test/gmg.jl

@@ -0,0 +1,50 @@
+import AMG: Level, MultiLevel, GaussSeidel
+
+function multigrid(A::SparseMatrixCSC{T,V}; max_levels = 10, max_coarse = 10,
+                    presmoother = GaussSeidel(), postsmoother = GaussSeidel()) where {T,V}
+
+    levels = Vector{Level{T,V}}()
+
+    while length(levels) + 1 < max_levels && size(A, 1) > max_coarse
+        A = extend!(levels, A)
+        #=if size(A, 1) <= max_coarse
+            # push!(levels, Level(A,spzeros(T,0,0),spzeros(T,0,0)))
+            break
+        end=#
+    end
+
+    MultiLevel(levels, A, presmoother, postsmoother)
+end
+
+function extend!(levels, A::SparseMatrixCSC{Ti,Tv}) where {Ti,Tv}
+
+    size_F = size(A, 1)
+    size_C = rem(size_F,2) == 0 ? div((size_F-1), 2) +1 : div((size_F-1), 2)
+    total_len = size_C + 2 * (size_C - 1)
+
+    I = Vector{Tv}(total_len)
+    J = Vector{Tv}(total_len)
+    V = Vector{Ti}(total_len)
+
+    l = 1
+    for k = 1:size_C
+        I[l], J[l], V[l] = 2k, k, 1
+        l += 1
+    end
+    for k = 1:size_C - 1
+        I[l], J[l], V[l] = 2k+1, k, 0.5
+        I[l+1], J[l+1], V[l+1] = 2k+1, k+1, 0.5
+        l += 2
+    end
+    
+    P = sparse(I, J, V, size_F, size_C)
+
+    R = transpose(P)
+
+    push!(levels, Level(A, P, R))
+
+    R * A * P
+end
+
+Base.show(io::IO, level::Level) = print(io, "Level")
+