COIN-OR::LEMON - Graph Library

Opened 6 months ago

Last modified 3 weeks ago

#622 new enhancement

unused variable in elevator.h

Reported by: zhaofeng-shu33 Owned by: Alpar Juttner
Priority: major Milestone: LEMON 1.4 release
Component: core Version: hg main
Keywords: Cc:
Revision id:

Description

There are some unused class private variables in elevator.h. For example, _items[i] for i > 0 (class Elevator); _item_num (class LinkedElevator?).

Change History (4)

comment:1 Changed 5 months ago by Alpar Juttner

The elements of _items are actually used through pointers. I agree it's a bit dirty. As far as I remember is it implemented this way for performance reasons.

On the other hand, _item_num is indeed unnecessary.

comment:2 Changed 5 months ago by zhaofeng-shu33

I check the latest file elevator.h again. _items[0] is used but _items[i] are not used throughout the source code.

Can I make a patch to this file or contribute something equivalent?

comment:3 Changed 5 months ago by Alpar Juttner

OK, I explain it in more details.

Syntactically, you could indeed replace std::vector<Item> _items with Item _item plus every instance of _items[0] with _item, and it would compile beautifully. But would crash immediately when trying to use it. Because the whole vector is indeed in heavy use through pointers.

In fact, it is a fundamental part of the data structure. It contains all items ordered by their levels and by there activeness. I.e. it stars with the active items on level 0, then the inactive ones on level 0, then the active ones on level 1, then the inactive ones on level 1 etc. The vectors _first and _last_active indicates the borders of these intervals on each level. In addition, the map _where gives a cross reference to the elements. The values of these vectors are pointers (Item *), and the elements of _items are accessed and manipulated through them.

Right at the beginning, initStart() puts all items into _item. Later on, its values are manipulated with the functions copy() and swap().

I hope this helped.

Version 0, edited 5 months ago by Alpar Juttner (next)

comment:4 Changed 3 weeks ago by zhaofeng-shu33

I understood now. Thank you very much.

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