Faster max off diag method (Thanks Andreas)

Author: ranjanan

src/classical.jl

@@ -67,7 +67,8 @@ function rs_direct_interpolation_pass1(S, A, splitting)
          if splitting[i] == C_NODE
              nnz += 1
          else
-            for jj = Sp[i]:Sp[i+1]-1
+            for jj = Sp[i]:Sp[i+1]
+                jj > length(Sj) && continue
                 if splitting[Sj[jj]] == C_NODE && Sj[jj] != i
                     nnz += 1
                 end
@@ -94,7 +95,6 @@ function rs_direct_interpolation_pass1(S, A, splitting)
     Bj = zeros(Ti, Bp[end])
     Bx = zeros(Float64, Bp[end])
     n_nodes = size(A, 1)
-    #Bp += 1
 
     for i = 1:n_nodes
         if splitting[i] == C_NODE
@@ -103,8 +103,8 @@ function rs_direct_interpolation_pass1(S, A, splitting)
         else
             sum_strong_pos = 0
             sum_strong_neg = 0
-            for jj = Sp[i]: Sp[i+1]-1
-                jj > length(Sp) && continue
+            for jj = Sp[i]: Sp[i+1]
+                jj > length(Sj) && continue
                 if splitting[Sj[jj]] == C_NODE && Sj[jj] != i
                     if Sx[jj] < 0
                         sum_strong_neg += Sx[jj]
@@ -118,7 +118,7 @@ function rs_direct_interpolation_pass1(S, A, splitting)
             sum_all_neg = 0
             diag = 0;
             for jj = Ap[i]:Ap[i+1]
-                jj > length(Ap) && continue
+                jj > length(Aj) && continue
                 if Aj[jj] == i
                     diag += Ax[jj]
                 else
@@ -138,8 +138,8 @@ function rs_direct_interpolation_pass1(S, A, splitting)
                 beta = 0
             end
 
-            neg_coeff = -alpha/diag;
-            pos_coeff = -beta/diag;
+            neg_coeff = -alpha / diag
+            pos_coeff = -beta / diag
 
             nnz = Bp[i]
             for jj = Sp[i]:Sp[i+1]
@@ -150,8 +150,8 @@ function rs_direct_interpolation_pass1(S, A, splitting)
                         Bx[nnz] = neg_coeff * Sx[jj]
                     else
                         Bx[nnz] = pos_coeff * Sx[jj]
-                        nnz += 1
                     end
+                    nnz += 1
                 end
             end
         end

src/strength.jl

@@ -33,13 +33,11 @@ function strength_of_connection{T}(c::Classical{T}, A::SparseMatrixCSC)
 end
 
 function find_max_off_diag(neighbors, col)
-    max_offdiag = 0
-    for (i,v) in enumerate(neighbors)
-        if col != i
-            max_offdiag = max(max_offdiag, abs(v))
-        end
+    maxval = zero(eltype(neighbors))
+    for i in 1:length(neighbors.nzval)
+        maxval = max(maxval, ifelse(neighbors.nzind[i] == col, 0, abs(neighbors.nzval[i])))
     end
-    max_offdiag
+    return maxval
 end
 
 function scale_cols_by_largest_entry(A::SparseMatrixCSC)