comment on t_wire_cost_map

Author: amin1377

vpr/src/route/router_lookahead_map.h

@@ -55,6 +55,10 @@ class Cost_Entry {
 
 /* provides delay/congestion estimates to travel specified distances
  * in the x/y direction */
+// This is a 6D array storing the cost to travel from a node of type CHANX/CHANY to a point that is dx, dy further, and is on the "layer_num" layer.
+// To store this information, the first index is the layer number that the node under consideration is on, the second index represents the type of channel (X/Y)
+// that the node under consideration belongs to, the third is the segment type (specified in the architecture file under the "segmentlist" tag), the fourth is the
+// "layer_num" mentioned above, the fifth is dx, and the last one is dy.
 typedef vtr::NdMatrix<Cost_Entry, 6> t_wire_cost_map; //[0..num_layers][0..1][[0..num_seg_types-1][0..num_layers][0..device_ctx.grid.width()-1][0..device_ctx.grid.height()-1]
                                                       //[0..1] entry distinguish between CHANX/CHANY start nodes respectively
                                                       // The first index is the layer number that the node under consideration is on, and the forth index