Hi, I am using Boost::Graph and DSP which comes with it to work out shortest paths around my graph. The problem is there is a certain exceptional situation when certain vertices can become unreachable along certain paths. I.e. although there is a valid distance value for edge B ? C, the same edge can become invalid if B is reached along a specific path. If this happens, I want DSP to reject that edge. I attempted to create a list of visitors. EdgeRelaxed records how vertices in the DSP queue were reached. EdgeExamined checks for the exceptional situation and if it's detected, it temporarily changes the distance value of the edge in question to infinity. EdgeNotRelaxed then restores the distance value to it's original. Unfortunately this approach doesn't seem to work, I think the reason for this is because dijkstras_shortest_paths() function gets information about distances from the weight_map which is passed to it. Is there any way I can modify the values inside the weight_map in between DSP stages to invalidate certain paths which will result in them being rejected for relaxation? Or perhaps there is an easier and tidier way of achieving the same result? Thanks in advance, Arty