[critical] Split row and column unused colors...

Author: amontoison

src/postprocessing.jl

@@ -49,29 +49,32 @@ function postprocess!(
         )
     end
 
-    if bicoloring
-        # Identify colors that are used in either the row or column partition
-        # color_used = row_color_used .| column_color_used
-        color_used .|= row_color_used
-    end
+    # if at least one of the colors is not used, modify the color assignments of vertices
+    has_neutral_color = bicoloring ? any(!, row_color_used) || any(!, column_color_used) : any(!, color_used)
+
+    if has_neutral_color
+        # size of the original matrix on which we want to perform coloring or bicoloring
+        (m, n) = g.original_size
 
-    # if at least one of the colors is useless, modify the color assignments of vertices
-    if any(!, color_used)
-        num_colors_useless = 0
+        # count the number of unused colors
+        num_unused_colors = 0
 
-        # determine what are the useless colors and compute the offsets
+        # count how many color indices are skipped before each color,
+        # in order to compact the color indexing after removing unused colors
         for ci in 1:nb_colors
-            if color_used[ci]
-                offsets[ci] = num_colors_useless
+            ci_required = bicoloring ? row_color_used[ci] || column_color_used[ci] : color_used[ci]
+            if ci_required
+                offsets[ci] = num_unused_colors
             else
-                num_colors_useless += 1
+                num_unused_colors += 1
             end
         end
 
-        # assign the neutral color to every vertex with a useless color and remap the colors
+        # replace unused colors by the neutral color and compact the remaining color indices
         for i in eachindex(color)
             ci = color[i]
-            if !color_used[ci]
+            ci_used = (i ≤ n) ? column_color_used[ci] : row_color_used[ci]
+            if !ci_used
                 # assign the neutral color
                 color[i] = 0
             else