[CHiPPS] Problems About Treeselection and Nodeselection in Alps

[化高峰]

Dear professors,
        I am puzzled about the Treeselection and Nodeselection in Alps.
        In I opinion selecting a node to process is the same with selecting a subtree.
        Because during the processing of the selected node the node becomes a subtree.
        But in the AlpsSearchStrategy.cpp there is Treeselection_ and nodeselection_.
        And even in the hybrid strategy, the Treeselection_ and the nodeselection_ are different.
        How do the two selection(Treeselection_ and Nodeselection_) work?
        I want to know this because:
        First I am trying to change search strategy when the tree-search is processing by reassign the value of nodeselection_ or treeselection_.
           Could I  change the value of one of them, change all of them, or can I give them different values(nodeselection_= new AlpsTreeSelectionBest; nodeSelection_ = new AlpsNodeSelectionDepth, for example)?
         Second, I will write my own hybrid at last, then how can I decide the value of treeselection_ and nodeselection?  
         And I checked doctor Xu's doctoral dissertation. There is only explanation about nodeselection_.
May happiness be with you!
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